U.S. patent application number 10/096414 was filed with the patent office on 2002-09-12 for optical transmitting apparatus and optical repeating apparatus.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Shirai, Katsuhiro.
Application Number | 20020126952 10/096414 |
Document ID | / |
Family ID | 14237158 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020126952 |
Kind Code |
A1 |
Shirai, Katsuhiro |
September 12, 2002 |
Optical transmitting apparatus and optical repeating apparatus
Abstract
In an optical amplifying technique using remote pumping, an
optical transmitting apparatus and an optical repeating apparatus
are provided. An optical repeating apparatus comprises a first
optical transmitting unit, a first loopback unit, a second optical
transmitting unit, a second loopback unit, and four optical
couplers, wherein transmission light and reception light are
transmitted through one optical fiber cable, whereby the
installation cost and maintenance cost of the optical cable are
decreased. Disconnect of the optical cable is detected by a
monitoring function using pumping light and residual pumping light,
whereby reliability and safety of the system are remarkably
improved. Additionally, adjustment of the optical output level of
the repeating station can be most suitably set according to an
actual transmission distance.
Inventors: |
Shirai, Katsuhiro;
(Kawasaki, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
700 11TH STREET, NW
SUITE 500
WASHINGTON
DC
20001
US
|
Assignee: |
FUJITSU LIMITED
Kawasaki
JP
|
Family ID: |
14237158 |
Appl. No.: |
10/096414 |
Filed: |
March 13, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10096414 |
Mar 13, 2002 |
|
|
|
PCT/JP99/06056 |
Oct 29, 1999 |
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Current U.S.
Class: |
385/24 ;
398/181 |
Current CPC
Class: |
H04B 10/075 20130101;
H04B 10/07 20130101; H04B 10/291 20130101; H04B 10/2972
20130101 |
Class at
Publication: |
385/24 ;
359/174 |
International
Class: |
G02B 006/28; H04B
010/02 |
Claims
1. An optical transmitting apparatus comprising: an optical
transmitting means for multiplexing and amplifying first
transmission light (.lambda.1L) and first pumping light
(.lambda.2PL) amplifying the first transmission light (.lambda.1L),
and outputting amplified optical signal to an internal optical
fiber; a level monitoring means connected to said optical
transmitting means for detecting a level of the optical signal
outputted from said optical transmitting means; an optical
multiplexing means connected to said internal optical fiber for
transmitting an optical signal in said internal optical fiber to a
first optical fiber connected to an external optical repeating
apparatus, and also being operable to receive an optical signal
having a predetermined wavelength in transmission light transmitted
from said external optical repeating apparatus through said first
optical fiber, and split the optical signal into a plurality of
directions, and output split optical signal; and a loopback light
detecting means connected to said optical multiplexing means for
receiving an optical monitoring signal transmitted from said
external optical repeating apparatus.
2. The optical transmitting apparatus according to claim 1 further
comprising a controlling means, connected to said optical
transmitting means, said level monitoring means and said loopback
light detecting means, for controlling an output level of the first
pumping light (.lambda.2PL) on the basis of a reception level of
the optical monitoring signal (.lambda.2PL') from said loopback
light detecting means.
3. The optical transmitting apparatus according to claim 2 further
comprising a disconnect detecting means disposed at an entrance
leading to said external optical repeating apparatus for detecting
that a fault occurs in said first optical fiber; said disconnect
detecting means comprising: a first transmitting side filter for
extracting residual pumping light (.lambda.3PR') from a received
optical signal, and outputting the residual pumping light
(.lambda.3PR'); a first transmitting side monitoring means for
detecting the residual pumping light (.lambda.3PR') from said first
transmitting filter; and a first transmitting side disconnect
detection outputting means for monitoring an operation of said
first transmitting side monitoring means to output information
relating to presence/absence of the residual pumping light
(.lambda.3PR').
4. An optical repeating apparatus comprising: a first optical
transmitting means for receiving first transmission light
(.lambda.1L) and first pumping light (.lambda.2PL) transmitted from
an optical transmitting apparatus through a first optical fiber,
amplifying the first transmission light (.lambda.1L) and the first
pumping light (.lambda.2PL), and outputting second transmission
light (.lambda.1L') and second pumping light (.lambda.2PL'); a
first loopback means, connected to said first optical transmitting
means, for extracting the second pumping light (.lambda.2PL') from
the optical signal amplified by said first optical transmitting
means, and outputting the second pumping light (.lambda.2PL'); a
second optical transmitting means for receiving third transmission
light (.lambda.1R) and third pumping light (.lambda.3PR)
transmitted from an optical receiving apparatus through said second
optical fiber, amplifying the third transmission light (.lambda.1R)
and the third pumping light (.lambda.3PR), and outputting fourth
transmission light (.lambda.1R'); a second loopback means,
connected to said second optical transmitting means, for extracting
fourth pumping light (.lambda.3PR') from the optical signal
amplified by said second optical transmitting means, and outputting
the fourth pumping light (.lambda.3PR'); a first optical coupler,
disposed on an output's side of said first optical transmitting
means, for outputting the second transmission light (.lambda.1L')
and the second pumping light (.lambda.2PL') toward the side of said
optical receiving apparatus, while outputting the third
transmission light (.lambda.1R) and the third pumping light
(.lambda.3PR) from the side of said optical receiving apparatus;
and a second optical coupler, disposed on an output's side of said
second optical transmitting means, for outputting the optical
signal from said first loopback means and the optical signal from
said second optical transmitting means toward a side of said
optical transmitting apparatus, while outputting the first
transmission light (.lambda.1L) and the first pumping light
(.lambda.2PL) from a side of said optical transmitting
apparatus.
5. The optical repeating apparatus according to claim 4, wherein
said first optical transmitting means receives the first
transmission light (.lambda.1L) and the first pumping light
(.lambda.2PL) transmitted from said optical transmitting apparatus
through said first optical fiber, changes either a level of the
first transmission light (.lambda.1L) or a level of the first
pumping light (.lambda.2PL) to a necessary level, amplifies changed
first transmission light (.lambda.1L) and first pumping light
(.lambda.2PL), and outputs the second transmission light
(.lambda.1L') and the second pumping light (.lambda.2PL'); said
second optical transmitting means receives the third transmission
light (.lambda.1R) and the third pumping light (.lambda.3PR)
transmitted from said optical receiving apparatus through said
second optical fiber, changes either a level of the third
transmission light (.lambda.1R) or a level of the third pumping
light (.lambda.3PR) to a necessary level, amplifies changed third
transmission light (.lambda.1R) or third pumping light
(.lambda.3PR), and outputs the fourth transmission light
(.lambda.1R').
6. The optical repeating apparatus according to claim 5, wherein
said first optical transmitting means comprises: a first pumping
light adjusting means for splitting the first transmission light
(.lambda.1L) and the first pumping light (.lambda.2PL), attenuating
a level of the pumping light (.lambda.2PL) by a necessary level,
and outputting the first transmission light (.lambda.1L) and the
first pumping light (.lambda.2PL); and said second optical
transmitting means comprises: a second pumping light adjusting
means for splitting the third transmission light (.lambda.1R) and
the third pumping light (.lambda.3PR), attenuating a level of the
pumping light (.lambda.3PR) by a necessary level, and outputting
the third transmission light (.lambda.1R) and the third pumping
light (.lambda.3PR).
7. The optical repeating apparatus according to claim 6, wherein
said first loopback means comprises a first optical detector for
detecting a level of the pumping light (.lambda.2PL') outputted
from said first optical amplifying means to control an attenuation
quantity of said first pumping light adjusting means on the basis
of a level value detected by said first optical detector; and said
second loopback means comprises a fourth optical detector for
detecting a level of the pumping light (.lambda.3PR") outputted
from said second optical amplifying means to control an attenuation
quantity of said second pumping light adjusting means on the basis
of a level value detected by said fourth optical detector.
8. The optical repeating apparatus according to claim 5, wherein
said first optical transmitting means comprises a first filter
disposed on an input's side of said first optical amplifying means
to remove the residual pumping light component (.lambda.3PR") from
a received optical signal; and said second optical transmitting
means comprises a third filter, disposed on an input's side of said
second optical amplifying means, for removing the residual pumping
light component (.lambda.2PL") from a received optical signal.
9. The optical repeating apparatus according to claim 6 further
comprising a first reception light monitoring means, disposed on an
entrance's side of said second optical fiber, for detecting a level
of a transmitted optical signal; said first reception light
monitoring means comprising: a sixth filter for extracting the
residual pumping light (.lambda.2PL") from the transmitted optical
signal, and outputting the residual pumping light (.lambda.2PL");
and a second optical detector for detecting a level of the residual
pumping light (.lambda.2PL") outputted from said sixth filter,
wherein an attenuation quantity of said first pumping light
adjusting means being controlled on the basis of a difference
between the level detected by said second optical detector and a
level beforehand prepared; and a second reception light monitoring
means, disposed on an entrance's side of said first optical fiber,
for detecting a level of a transmitted optical signal; said second
reception light monitoring means comprising: a fifth filter for
extracting the residual pumping light (.lambda.3PR") from the
transmitted optical signal and outputting the residual pumping
light (.lambda.3PR"); and a third optical detector for detecting a
level of the residual pumping light (.lambda.3PR") outputted from
said fifth filter, wherein an attenuation quantity of said second
pumping light adjusting means being controlled on the basis of a
difference between the level detected by said third optical
detector and a level beforehand prepared.
10. The optical repeating apparatus according to claim 9 further
comprising: a second filter disposed on an output's side of said
first optical amplifying means, for extracting first pumping light
(.lambda.4PT) outputted from said first optical amplifying means; a
first optical detector for detecting a level of first pumping light
(.lambda.4PT) outputted from said second filter; an eighth filter
for extracting the residual pumping light (.lambda.7PT) from a
received optical signal and outputting the residual pumping light
(.lambda.7PT); and a sixth optical detector for detecting the
residual pumping light (.lambda.7PT) from said eighth filter,
wherein an output level of said first optical amplifying means
being controlled on the basis of a detected level of said first
optical detector, a detected level of said second optical detector
and a detected level of said sixth optical detector; a fourth
filter, disposed on an output's side of said second optical
amplifying means, for extracting the second pumping light
(.lambda.5PT) outputted from said second optical amplifying means;
a fourth optical detector for detecting a level of the second
pumping light (.lambda.5PT) outputted from said fourth filter; a
seventh filter for extracting the residual pumping light
(.lambda.2PL) from a received optical signal and outputting the
residual pumping light (.lambda.2PL); and a fifth optical detector
for detecting the residual pumping light (.lambda.2PL) from said
seventh filter, wherein an output level of said second optical
amplifying means being controlled on the basis of a detected level
of said fourth optical detector, a detected level of said third
optical detector and a detected level of said fifth optical
detector.
11. The optical repeating apparatus according to claim 5, wherein
said first optical transmitting means comprises: a first displaying
means having control data relating to a first transmission loss
value of an optical signal loss on a transmission path, and being
operable to output the control data; and a first pumping light
controlling means for controlling an output level of a first
pumping source of its own station on the basis of the control data
of said first displaying means; said second optical transmitting
means comprises: a second displaying means having control data
relating to a second transmission loss value of an optical signal
loss on a transmission path, and being operable to output the
control data; and a second pumping light controlling means for
controlling an output level of said second pumping source of its
own station on the basis of the control data of said second
displaying means.
12. The optical repeating apparatus according to claim 9, wherein
said first pumping light controlling means comprises a first level
monitoring means, disposed on an output's side of said second
filter, for detecting a level of the second pumping light
(.lambda.2PL) outputted from said second filter, and controlling an
output optical level of said first pumping source on the basis of
the level detected by said first level monitoring means and a
reception light level detected by said first reception light
monitoring means; and said second pumping light controlling means
comprises a fourth optical detector, disposed on an output's side
of said fourth filter, for detecting a level of the third pumping
light (.lambda.3PR) outputted from said fourth filter, and
controlling an output optical level of said second pumping source
on the basis of the level value detected by said fourth optical
detector and a reception light level detected by said second
reception light monitoring means.
13. The optical repeating apparatus according to claim 11, wherein
said first pumping light controlling means controls an output of
said first pumping source on the basis of a level of the first
pumping light (.lambda.2PL) and a level of the residual pumping
light (.lambda.7PL) from said optical receiving apparatus; and said
second pumping light controlling means controls an output of said
second pumping source on the basis of a level of the second pumping
light (.lambda.2PR) and a level of the residual pumping light
(.lambda.2PL) from a side of said optical transmitting
apparatus.
14. The optical repeating apparatus according to claim 4 further
comprising a first disconnect detecting means, disposed on an
entrance's side of said first optical fiber for detecting
disconnect of said first optical fiber, and a second disconnect
detecting means, disposed on an entrance's side of said second
optical fiber, for detecting disconnect of said second optical
fiber; said first disconnect detecting means comprising: a seventh
filter for extracting residual pumping light (.lambda.2PL') from a
received optical signal and outputting the residual pumping light
(.lambda.2PL'); a fifth optical detector for detecting the residual
pumping light (.lambda.2PL') from said seventh filter; a first
disconnect detection outputting means for monitoring an operation
of said fifth optical detector to output information relating to
presence/absence of the residual pumping light (.lambda.2PL'); said
second disconnect detecting means comprising: an eighth filter for
extracting the residual pumping light (.lambda.7PT) from a received
optical signal, and outputting the residual pumping light
(.lambda.7PT) a sixth optical detector for detecting the residual
pumping light (.lambda.7PT) from said eighth filter; and a second
disconnect detection outputting means for monitoring the operation
of said sixth optical detector to output information relating to
presence/absence of the residual pumping light (.lambda.7PT).
15. The optical repeating apparatus according to claim 14 further
comprising: a reflecting means, disposed on an input's side of said
first optical amplifying means, for reflecting an optical signal
(.lambda.2PL) at a specific wavelength contained in a received
optical signal; a first reflected light receiving means, disposed
on an input's side of said first optical amplifying means for
detecting residual pumping light (.lambda.5PT) contained in a
received optical signal, and detecting a level of the residual
pumping light (.lambda.5PT); a reflecting means, disposed on an
input's side of said second optical amplifying means, for
reflecting an optical signal (.lambda.7PT) at a specific wavelength
contained in a received optical signal; and a second reflected
light receiving means, disposed on an input's side of said second
optical amplifying means, for detecting residual pumping light
(.lambda.4PL) contained in a received optical signal, and detecting
a level of the residual pumping light (.lambda.4PT).
16. The optical repeating apparatus according to claim 15 further
comprising: a second filter, disposed on an output's side of said
first optical amplifying means, for extracting the first pumping
light (.lambda.4PT), and outputting the first pumping light
(.lambda.4PT); a first optical detector for displaying a level of
the first transmission light (.lambda.4PT) outputted from said
second filter; a fourth filter, disposed on an output's side of
said second optical amplifying means, for extracting the second
pumping light (.lambda.5PT), and outputting the second pumping
light (.lambda.5PT); and a fourth optical detector for displaying a
level of the second transmission light (.lambda.5PT) extracted by
said fourth filter.
17. The optical repeating apparatus according to claim 15 further
comprising: a reflecting means, disposed on an input's side of said
first filter, for reflecting light at a specific wavelength
contained in a received optical signal; a fifth filter for
extracting the residual pumping light (.lambda.5PT) from an optical
signal from a side of said optical transmitting apparatus, and
outputting the residual pumping light (.lambda.5PT); a third
optical detector for detecting the residual pumping light
(.lambda.5PT) from said fifth filter; a seventh filter for
extracting the residual pumping light (.lambda.2PL) from an optical
signal from a side of said optical transmitting apparatus, and
outputting the residual pumping light (.lambda.2PL); a fifth
optical detector for detecting the residual pumping light
(.lambda.2PL) outputted from said seventh filter; a reflecting
means, disposed on an input's side of said third filter, for
reflecting light having a specific wavelength; a sixth filter for
extracting the residual pumping light (.lambda.4PT) from an optical
signal from a side of said optical receiving apparatus, and
outputting the residual pumping light (.lambda.4PT); a second
optical detector for detecting the residual pumping light
(.lambda.4PT) from said sixth filter; an eighth filter for
extracting the residual pumping light (.lambda.7PT) from an optical
signal from a side of said optical receiving apparatus, and
outputting the residual pumping light (.lambda.7PT); and a sixth
optical detector for detecting the residual pumping light
(.lambda.7PT) outputted from said eighth filter.
18. The optical repeating apparatus according to claim 17 further
comprising: a second filter, disposed on an output's side of said
first optical amplifying means, for extracting the first pumping
light (.lambda.4PT) outputted from said first optical amplifying
means; a first optical detector for detecting a level of the first
pumping light (.lambda.4PT) outputted from said second filter; a
fourth filter, disposed on an output's side of said second optical
amplifying means, for extracting the second pumping light
(.lambda.5PT) outputted from said second optical amplifying means;
and a fourth optical detector for detecting a level of the second
pumping light (.lambda.5PT) outputted from said fourth filter.
19. The optical repeating apparatus according to claim 7 further
comprising: a second alarm signal communication controlling means
for outputting a port switching signal when detecting that the
residual pumping light (.lambda.2PL) is not inputted to said fifth
optical detector, to superimpose a modulation signal on second
pumping source and output superimposed pumping light; a first
optical switch connected to said second pumping source to be
operable to select according to the port switching signal outputted
from said second alarm signal communication controlling means
whether the second pumping light (.lambda.5PT) from said second
pumping source is led to an input's side of said second optical
amplifying means or the second pumping light (.lambda.5PT) on which
the modulation signal has been superimposed is led to an output's
side of said second optical amplifying means; a first alarm signal
detecting means, connected to said third optical detector, for
detecting the second pumping light (.lambda.5PT), on which the
modulation signal has been superimposed, looped back and inputted
from said optical transmitting apparatus, and outputting a first
alarm signal to an outside; a second disconnect detecting means for
detecting that the first alarm signal is outputted from said first
alarm signal detecting means; a second alarm signal communication
controlling means for outputting a port switching signal when
detecting that the residual pumping light (.lambda.7PT) is not
inputted to said sixth optical detector, to superimpose a
modulation signal on said first pumping source and output
superimposed pumping light; a second optical switch connected to a
first pumping source to be operable to select according to the port
switching signal outputted from said second alarm signal
communication controlling means whether first pumping light
(.lambda.4PT) from said first pumping source is led to an input's
side of said first optical amplifying means or the first pumping
light (.lambda.4PT) on which the modulation signal has been
superimposed is led to an output's side of said first optical
amplifying means; a second alarm signal detecting means, connected
to said second optical detector, for detecting the first pumping
light (.lambda.4PT), on which the modulation signal has been
superimposed, returned and inputted from said optical receiving
apparatus, and outputting a second alarm signal to the outside; and
a fourth disconnect detecting means for detecting that the second
alarm signal is outputted from said second alarm signal detecting
means.
20. The optical repeating apparatus according to claim 19 further
comprising: a second filter disposed on an output's side of said
first optical amplifying means to extract the first pumping light
(.lambda.4PT) outputted from said first optical amplifying means; a
first optical detector for detecting a level of the first pumping
light (.lambda.4PT) outputted from said second filter; a fourth
filter, disposed on an output's side of said second optical
amplifying means, for extracting second pumping light (.lambda.5PT)
outputted from said second optical amplifying means; and a fourth
optical detector for detecting a level of the second pumping light
(.lambda.5PT) outputted from said fourth filter.
21. The optical repeating apparatus according to claim 7 further
comprising: a first optical detector, disposed on an output's side
of said first optical amplifying means, for detecting a level of
first pumping light (.lambda.c) outputted from said first optical
amplifying means; a second alarm signal detecting means for
detecting the first pumping light (.lambda.c), on which a
modulation signal has been superimposed, sent from a side of said
optical receiving apparatus, and outputting a first alarm signal to
an outside; a fourth optical detector, disposed on an output's side
of said second optical amplifying means, for detecting a level of
second pumping light (.lambda.d) outputted from second optical
amplifying means; a first alarm signal detecting means for
detecting the second pumping light (.lambda.d), on which a
modulation signal has been superimposed, sent from a side of said
optical transmitting apparatus, and outputting a second alarm
signal to the outside; a first alarm signal communication
controlling means for outputting a port switching signal when
detecting that first residual pumping light (.lambda.f) sent from
said optical receiving apparatus is not inputted, to superimpose a
modulation signal on first pumping source and output it; a second
optical switch connected to said first pumping source to be
operable to select according to the port switching signal outputted
from said first alarm signal communication controlling means
whether the first pumping light (.lambda.c) from said first pumping
source is led to an input's side of said first optical amplifying
means or the first pumping light (.lambda.c) on which the
modulation signal has been superimposed is led to an output's side
of said first optical amplifying means; a second alarm signal
communication controlling means for outputting a port switching
signal when detecting that second residual pumping light
(.lambda.dT) sent from a side of said optical transmitting
apparatus is not inputted, in order to superimpose a modulation
signal on second pumping source and output superimposed pumping
light; and a first optical switch connected to said second pumping
source to be operable to select according to the port switching
signal outputted from said second alarm signal communication
controlling means whether the second pumping light (.lambda.d) from
said second pumping source is led to an input's side of said second
optical amplifying means or the second pumping light (.lambda.d) on
which the modulation signal has been superimposed is led to an
output's side of said second optical amplifying means.
Description
TECHNICAL FIELD
[0001] The present invention relates to an optically amplified
transmission apparatus and a repeater of a remote pumping type in
an optical two-way transmission system, for example. Particularly,
the present invention relates to an optical transmitting apparatus
and an optical repeating apparatus suitable for use in a system
which can transmit transmission-reception light and pumping light
through optical fiber cables in one system, remotely control the
output level of a pumping source, fulfil an optical level
controlling function, a disconnect detecting function and an
automatic restoring function for an optical cable among the
stations.
BACKGROUND ART
[0002] Long distant transmission using optical fiber cables
(hereinafter referred as optical cables, occasionally) is performed
in order to transmit a large volume of data at a high speed, in
recent years. In the long distance transmission, a transmission
loss generates in an optical cable. For this, the optically
amplified transmission system transmits transmission light and
reception light thorugh different optical cables in order to
compensate it.
[0003] The optically amplified transmission system can remotely
control an amplification level of an optical amplifier in the
optical repeater. When the optical cables are installed undersea,
for example, it is possible to remotely adjust the amplification
level using an optical cable instead the administrator adjusts the
amplification level by hands. Concretely, this adjustment is
carried out by inputting pumping light to the optical amplifier,
which is called the optical pumping system. In the optical pumping
system, the pumping light of a transmission path terminal station
is transmitted to an optical repeater, the transmitted pumping
light and transmission light are multiplexed in the optical
repeater, whereby optical repeating is performed.
[0004] In order to perform the optical repeating, a different
optical cable from optical cables through which the transmission
light and the pumping light are transmitted is installed, and these
optical cables are prepared for each repeater to transmit optical
signals. These repeaters are connected by the optical cables.
[0005] When a fault occurs in the optical cable and the optical
cable is cut, it is necessary to specify the cut position and
restore it. Detection of cut of an optical cable is called
disconnect detection of an optical cable. The disconnect detecting
function is dispensable.
[0006] FIG. 47 is a diagram showing an example of the optically
amplified transmission system using the remote pumping optically
amplifying system. An optically amplified transmission system 90
shown in FIG. 47 is described in Japanese Patent Laid-Open
Publication No. 9-113941 in which a technique is disclosed, which
can further extend a transmission distance of optical signals using
an optically amplifying system which can do remote pumping.
[0007] The optically amplified transmission system 90 shown in FIG.
47 comprises a transmitting station (transmitting terminal) 90a, a
receiving station (receiving terminal) 90b, a plurality (three, for
example) of repeating stations 90c, and a plurality (three, for
example) of repeating stations 90d between them. Optical cables in
two systems are used for transmission and reception.
[0008] The transmitting station 90a comprises a transmitting unit
91a and a receiving unit 91b. The receiving station 90b comprises a
transmitting unit 91d and a receiving unit 91c, as well. The
transmitting unit 91a and the receiving unit 91d comprise a signal
light source 92a and a plurality of pumping sources 92b. Each of
the transmitting station 90a and the receiving station 90b prepares
the pumping sources 92b in different systems from that of the
signal light source in order to perform remote pumping, whereby
pumping light is transmitted from a terminal station to a repeater
through an optical cable differing from an optical cable for
transmission-reception light between the transmitting station 90a
and the receiving station 90b.
[0009] Japanese Patent Laid-Open Publication No. 9-200144 discloses
an optically amplified repeating system which can suppress the
output level of a repeater apparatus to realize a long repeater
spacing. According to the technique disclosed in this publication,
it is possible to extend the repeating distance.
[0010] However, the techniques disclosed in Japanese Patent
Laid-Open Publication No. 9-113941 and Japanese Patent Laid-Open
Publication No. 9-200144 have three types of problems. First, since
a plurality of pumping sources are transmitted through optical
cables differing from an optical cable through which optical
signals are transmitted, the investment cost of the optical cables
is high. In concrete, in the optically amplified transmission
system 90 shown in FIG. 47, the number of the optical cables
required among the optical repeaters is two to three, and the
number of optical cables required between the terminal stations is
14 for both transmission and reception. Further, no description of
the optical level controlling method is seen therein.
[0011] Further, in remote pumping, adjustment of the output level
between the optical repeaters sometimes lacks accuracy since the
adjustment is carried out on the basis of theoretical optical
transmission distance calculation. The second problem is that a
precise control is necessary in each terminal station, which
requires a labor cost of an administrator who executes the
control.
[0012] The third problem is that the method for detecting cut of an
optical cable is not established.
[0013] In the light of the above problems, the first object of the
present invention is to enable transmission and reception of
transmission light and reception light through one optical fiber
cable, thereby decreasing the installation cost and maintenance
cost of the optical cables.
[0014] The second object of the present invention is to detect cut
of the optical cable by a monitoring function using pumping light
and residual pumping light, thereby largely improving reliability
and safety of the system. The third object of the present invention
is to most suitably set optical output level adjustment in the
repeating station according to an actual transmitting distance.
DISCLOSURE OF INVENTION
[0015] For this, an optical transmitting apparatus of this
invention comprises an optical transmitting means for multiplexing
and amplifying first transmission light (.lambda.1L) and first
pumping light (.lambda.2PL) amplifying the first transmission light
(.lambda.1L), and outputting amplified optical signal to an
internal optical fiber, a level monitoring means connected to the
optical transmitting means for detecting a level of the optical
signal outputted from the optical transmitting means, an optical
multiplexing means connected to the internal optical fiber for
transmitting an optical signal in the internal optical fiber to a
first optical fiber connected to an external optical repeating
apparatus, and also being operable to receive an optical signal
having a predetermined wavelength in transmission light transmitted
from the external optical repeating apparatus through the first
optical fiber, and split the optical signal into a plurality of
directions, and output split optical signal, and a loop back light
detecting means connected to the optical multiplexing means for
receiving an optical monitoring signal (.lambda.2PL') transmitted
from the external optical repeating apparatus.
[0016] Accordingly, transmission light and reception light can be
transmitted through optical fiber cables in one system, so that the
installation cost and maintenance cost of an optical cable cost can
be decreased. Since cut of the optical cable is performed by a
monitoring function using pumping light and residual pumping light
in a two-way transmission, reliability and safety of the system can
be remarkably improved.
[0017] An optical repeating apparatus of this invention comprises a
first optical transmitting means for receiving first transmission
light (.lambda.1L) and first pumping light (.lambda.2PL)
transmitted from an optical transmitting apparatus through a first
optical fiber, amplifying the first transmission light (.lambda.1L)
and the first pumping light (.lambda.2PL), and outputting second
transmission light (.lambda.1L') and second pumping light
(.lambda.2PL'), a first loopback means connected to the first
optical transmitting means to extract the second pumping light
(.lambda.2PL') from the optical signal amplified by the first
optical transmitting means, and outputting the second pumping light
(.lambda.2PL'), a second optical transmitting means for receiving
third transmission light (.lambda.1R) and third pumping light
(.lambda.3PR) transmitted from an optical receiving apparatus
through the second optical fiber, amplifying the third transmission
light (.lambda.1R) and the third pumping light (.lambda.3PR), and
outputting fourth transmission light (.lambda.1R'), a second
loopback means connected to the second optical transmitting means
to extract fourth pumping light (.lambda.3PR') from the optical
signal amplified by the second optical transmitting means, and
outputting the fourth pumping light (.lambda.3PR'), a first optical
coupler disposed on an output's side of the first optical
transmitting means to output the second transmission light
(.lambda.1L') and the second pumping light (.lambda.2PL') toward
the optical receiving apparatus, while outputting the third
transmission light (.lambda.1R) and the third pumping light
(.lambda.3PR) from the optical receiving apparatus, and a second
optical coupler disposed on an output's side of the second optical
transmitting means to output the optical signal from the first
loopback means and the optical signal from the second optical
transmitting means toward a side of the optical transmitting
apparatus, while outputting the first transmission light
(.lambda.1L) and the first pumping light (.lambda.2PL) from a side
of the optical transmitting apparatus.
[0018] Accordingly, optical output level adjustment in the
repeating station is most suitably set according to an actual
transmission distance, which allows an efficient system
operation.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a diagram showing a structure of an optical
amplification two-way transmission remote pumping system according
to a first embodiment of this invention;
[0020] FIG. 2 is a diagram showing an internal structure of a
repeating station according to the first embodiment of this
invention;
[0021] FIG. 3 is a diagram showing a structure of an optical system
according to a first modification of the first embodiment of this
invention;
[0022] FIG. 4 is a diagram showing an internal structure of a first
repeating station according to the first modification of the first
embodiment of this invention;
[0023] FIG. 5 is a diagram showing a structure of an optical system
according to a second modification of the first embodiment of this
invention;
[0024] FIG. 6 is a diagram showing an internal structure of a first
repeating station according to the second modification of the first
embodiment of this invention;
[0025] FIG. 7 is a diagram showing a structure of an optical system
according to a third modification of the first embodiment of this
invention;
[0026] FIG. 8 is a diagram showing a structure of a first repeating
station according to the third modification of the first embodiment
of this invention;
[0027] FIG. 9 is a diagram showing a structure of an optical system
according to a fourth modification of the first embodiment of this
invention;
[0028] FIG. 10 is a diagram showing an internal structure of a
first repeating station according to the fourth modification of the
first embodiment of this invention;
[0029] FIG. 11 is a diagram showing an internal structure of a
second repeating station according to the fourth modification of
the first embodiment of this invention;
[0030] FIG. 12 is a diagram showing a structure of an optical
system according to a fifth modification of the first embodiment of
this invention;
[0031] FIG. 13 is diagram showing a structure of a first repeating
station according to the fifth modification of the first embodiment
of this invention;
[0032] FIG. 14 is a diagram showing an internal structure of a
second repeating station according to the fifth modification of the
first embodiment of this invention;
[0033] FIG. 15 is a diagram showing a structure of an optical
system according to a sixth modification of the first embodiment of
this invention;
[0034] FIG. 16 is a diagram showing an internal structure of a
first repeating station according to the sixth modification of the
first embodiment of this invention;
[0035] FIG. 17 is a diagram showing an internal structure of a
second repeating station according to the sixth modification of the
first embodiment of this invention;
[0036] FIG. 18 is a diagram showing an internal structure of a
first repeating station according to a seventh modification of the
first embodiment of this invention;
[0037] FIG. 19 is a diagram showing an internal structure of a
second repeating station according to the seventh modification of
the first embodiment of this invention;
[0038] FIG. 20 is a diagram showing an internal structure of a
first repeating station according to an eighth modification of the
first embodiment of this invention;
[0039] FIG. 21 is a diagram showing a structure of an optical
system according to a ninth modification of the first embodiment of
this invention;
[0040] FIG. 22 is a diagram showing an internal structure of a
first repeating station according to the ninth modification of the
first embodiment of this invention;
[0041] FIG. 23 is a diagram showing an internal structure of a
second repeating station according to the ninth modification of the
first embodiment of this invention;
[0042] FIG. 24 is a diagram showing a structure of an optical
system according to a tenth modification of the first embodiment of
this invention;
[0043] FIG. 25 is a diagram showing an internal structure of a
first repeating station according to the tenth modification of the
first embodiment of this invention;
[0044] FIG. 26 is a diagram showing an internal structure of a
second repeating station according to the tenth modification of the
first embodiment of this invention;
[0045] FIG. 27 is a diagram showing a structure of an optical
system according to a second embodiment of this invention;
[0046] FIG. 28 is a diagram showing an internal structure of a
first repeating station according to the second embodiment of this
invention;
[0047] FIG. 29 is a diagram showing an internal structure of a
second repeating station according to the second embodiment of this
invention;
[0048] FIG. 30 is a diagram showing a structure of an optical
system according to a first modification of the second embodiment
of this invention;
[0049] FIG. 31 is a diagram showing an internal structure of a
first repeating station according to the first modification of the
second embodiment of this invention;
[0050] FIG. 32 is a diagram showing an internal structure of a
second repeating station according to a first modification of the
second embodiment of this invention;
[0051] FIG. 33 is a diagram showing a structure of a first
repeating station according to a second modification of the second
embodiment of this invention;
[0052] FIG. 34 is a diagram showing a structure of an optical
system according to a third modification of the second embodiment
of this invention;
[0053] FIG. 35 is a diagram showing an internal structure of a
first repeating station according to the third modification of the
second embodiment of this invention;
[0054] FIG. 36 is a diagram showing a structure of an optical
system according to a third embodiment of this invention;
[0055] FIG. 37 is a diagram showing a structure of a first
repeating station according to the third embodiment of this
invention;
[0056] FIG. 38 is a diagram showing a structure of an optical
system according to a first modification of the third embodiment of
this invention;
[0057] FIG. 39 is a diagram showing an internal structure of a
first repeating station according to the first modification of the
third embodiment of this invention;
[0058] FIG. 40 is a diagram showing a structure of an optical
system according to a second modification of the third embodiment
of this invention;
[0059] FIG. 41 is a diagram showing an internal structure of a
first repeating station according to the second modification of the
third embodiment of this invention;
[0060] FIG. 42 is a diagram showing an internal structure of a
second repeating station according to the second modification of
the third embodiment of this invention;
[0061] FIG. 43 is a diagram showing a structure of an optical
system according to a third modification of the third embodiment of
this invention;
[0062] FIG. 44 is a diagram showing an internal structure of a
first repeating station according to the third modification of the
third embodiment of this invention;
[0063] FIG. 45 is a diagram showing a structure of an optical
system according to a fourth modification of the third embodiment
of this invention;
[0064] FIG. 46 is a diagram showing an internal structure of a
first repeating station according to the fourth modification of the
third embodiment of this invention; and
[0065] FIG. 47 is a diagram showing an example of optical
communication system using a remote pumping light optical
amplification system.
BEST MODE FOR CARRYING OUT THE INVENTION
[0066] (A) Description of First Embodiment of the Invention
[0067] FIG. 1 is a diagram showing a structure of an optically
amplified two-way transmission remote pumping system according to a
first embodiment of this invention. An optically amplified two-way
transmission remote pumping system 10 shown in FIG. 1 is a system
which can transmit/receive transmission light, reception light and
pumping light through optical fiber cables of one system.
[0068] The optical system 10 shown in FIG. 1 comprises a
transmitting station (A station) 20, a repeating station 30, and a
receiving station (B station) 40, where the stations are connected
by optical cables to be able to transmit optical signals in two
ways. In the repeating station 30, the output level of a pumping
source thereof is controlled. Between the stations, a control on
the optical level and detection of cut of the optical cable are
carried out, whereby the system can be automatically restored. In
the following descriptions, the optically amplified two-way
transmission remote pumping system will be occasionally referred as
an optical system.
[0069] In FIG. 1, wavelengths of optical signals used among the
transmitting station 20, the repeating station 30 and the receiving
station 40 areas follows. Wavelength of optical signals
(transmission light) sent from the transmitting station 20 to the
repeating station 30 is of two types; .lambda.1L and .lambda.2PL.
Wavelengths of optical signals sent from the repeating station 30
to the transmitting station 20 are of three types; .lambda.1L',
.lambda.3PR' and .lambda.2L'.
[0070] In the wavelengths of the transmission light from the
transmitting station 20 to the repeating station 30, .lambda.1L is
a wavelength component of signal light on which a signal component
has been superimposed, and .lambda.2PL is a wavelength component of
a first pumping source (Pump LD or PLD; Pump Laser Diode) 22d to be
described later. On the other hand, in the wavelengths of
transmission light from the repeating station 30 to the
transmitting station 20, .lambda.1R' is a wavelength component of
signal light on which a signal component has been superimposed, and
.lambda.3PR' and .lambda.2PL' are wavelength components of two
types of pumping sources in the repeating station 30. Optical
signals having these wavelength components become monitor light,
and are inputted to the transmitting station 20.
[0071] Meanwhile, with respect to subscripts of the wavelengths, L
represents local, whereas R represents remote. Here, "local"
signifies the transmitting station 20 that is a local station,
whereas "remote" signifies the receiving station 40 that is a
remote station. These subscripts will be used in the same meanings
in the following descriptions.
[0072] The transmitting station 20 in FIG. 1 is a transmitting
terminal station which transmits/receives optical signals. The
transmitting station 20 comprises an optical transmitting means 22,
a level monitoring means 23, an optical coupler (ODC: Optical
Directional Coupler) 51, a loopback light detecting means 24, a
controlling means (control unit) 25 and an optical receiving means
21.
[0073] The optical transmitting means 22 multiplexes a first
transmission light (.lambda.1L) and first pumping light
(.lambda.2PL) amplifying the first transmission light (.lambda.1L),
amplifies them, and outputs the amplified optical signal to an
internal optical fiber. The optical transmitting means 22 comprises
a transmitting unit 22a, a first pumping source (pumping source 21)
22d, an optical amplifier 22b, and an isolator 22c. The internal
optical fiber is installed inside the transmitting station 20,
which will be sometimes used to differentiate it from an optical
cable installed in the transmission section in the following
descriptions.
[0074] The transmitting unit 22a electro-optically converts a voice
signal or a data signal on the telephone, for example, sent from
another network, and outputs it, which is referred as an OS
(Optical Sending Unit) In the following descriptions, assuming that
a voice signal or the like on the telephone is transmitted and
received. The first pumping source 22d generates first pumping
light (.lambda.2PL). The optical amplifier 22b amplifies an optical
signal, an EDFA (Erbium-Doped Fiber Amplifier) being used therefor.
The isolator 22c sends an optical signal inputted from the optical
amplifier 22b to the optical coupler 51, while absorbing power of
an optical signal leaking from the optical coupler 51 to prevent
the optical signal from flowing into the optical amplifier 22b.
[0075] Whereby, the optical signal outputted from the transmitting
unit 22a and the first pumping light (.lambda.2PL) from the first
pumping source 22d are optically amplified by the optical amplifier
22b, and the optically amplified optical signal is sent to the
optical coupler 51 through the isolator 22c.
[0076] The level monitoring means 23 is connected to the optical
transmitting means 22 to detect a level of the optical signal
outputted from the optical transmitting means 22. The level
monitoring means 23 comprises a second filter (filter 2) 23a, and a
first optical detector (photodiode 1) 23b. The second filter 23a
extracts only the .lambda.2PL component in the optical signal
(.lambda.1L+.lambda.2PL) outputted from the optical transmitting
means 22, and outputs it. This function is realized by, for
example, an optical filter. The first optical detector 23b detects
an output from the second filter 23a, a function of which is
realized by, for example, a photodiode. Incidentally, the optical
signal (.lambda.1L+.lambda.2PL) signifies an optical signal having
a wavelength .lambda.1L and a wavelength .lambda.2PL. The similar
expression will be sometimes used in the following
descriptions.
[0077] The optical coupler 51 is connected to the internal optical
fiber to transmit the optical signal in the internal optical fiber
to a first optical fiber connected to the repeating station 30
(external optical repeating apparatus), while being able to receive
an optical signal having a predetermined wavelength in an optical
signal transmitted from the repeating station 30 through the first
optical fiber to branch the optical signal into a plurality of
directions and output it. The optical coupler 51 thus multiplexes
and demultiplexes the optical signals. In concrete, an optical
fiber of a fusion type with 1.times.3 terminals is used for the
optical coupler 51. An optical signal is inputted from one
terminal, and outputted as the same optical signal from each of the
three terminals. On the other hand, optical signals are inputted
from the three terminals, and outputted as the same optical signal
from one terminal. The first optical fiber signifies an optical
fiber transmitting optical signals sent from the transmitting
station's side. Whereby, transmission light and reception light can
be transmitted through one optical cable.
[0078] The loopback light detecting means 24 is connected to the
optical coupler 51 to receive an optical monitoring signal
(.lambda.2PL') transmitted from the repeating station 30. The
loopback light detecting means 24 comprises a fifth filter (filter
5) 24a and a second optical detector (photodiode 2) 24b. The
optical monitoring signal is an optical signal transmitted from the
adjacent repeating station 30, as will be described later, used to
monitor a state of transmission in the optical cable. The fifth
filter 24a extracts only the .lambda.2PL' component in the optical
signal (.lambda.1R'+.lambda.3PR'+.lambda.2PL') from the repeating
station outputted from the optical coupler 51, and outputs it, a
function of which is realized by, for example, an optical filter.
The second optical detector 24b detects an output from the fifth
filter 24a, a function of which is realized by, for example, a
photodiode.
[0079] The controlling means 25 is connected to the optical
transmitting means 22, the level monitoring means 23 and the
loopback light detecting means 24 to control the output level of
the first pumping light (.lambda.2PL) on the basis of a reception
level of the optical monitoring signal (.lambda.2PL') from the
loopback light detecting means 24.
[0080] Only the .lambda.2PL component is extracted from the optical
signal outputted from the optical transmitting means 22 by the
second filter 23a, an output from the second filter 23a is detected
by the first optical detector 23b, the optical monitoring signal
(.lambda.2PL') transmitted from the repeating station 30 is
received by the loopback light detecting means 24, the .lambda.2PL
component and the .lambda.2PL' component are inputted to the
controlling means 25, and the output level of the first pumping
light (.lambda.2PL) is controlled by the controlling means 25 on
the basis of the reception levels of these components, and adjusted
to the optimum output power.
[0081] The optical receiving means 21 is connected to the optical
coupler 51 to receive an optical signal transmitted from the
repeating station 30. The optical receiving means 21 comprises a
first filter (filter 1) 21b and a receiving unit 21a. The first
filter 21b extracts only a .lambda.1R' component in an optical
signal from the optical coupler 51. The receiving unit 21a receives
an optical signal having the .lambda.1R' component from the first
filter 21b, electro-optically converts the optical signal, and
sends, for example, a voice signal or a data signal on the
telephone to another network (not shown). The receiving unit is
sometimes called an OR (Optical Receiving Unit).
[0082] Accordingly, the transmitting station 20 has three kinds of
functions; a transmitting function, a receiving function and a
monitoring function. An optical signal to be transmitted is
outputted to the optical cable, and an optical signal and monitor
light send from the repeating station 30 are inputted to the same
optical cable. In the transmitting station 20, the administrator
sets the pumping level of an optical signal to be sent to an
appropriate value to control it, on the basis of the monitor
light.
[0083] As this, it is possible to transmit/receive through the
optical cables in one system, and remotely adjust the output level
of the pumping light in the repeating station 30.
[0084] The repeating station (repeater) 30 is provided on a
transmission path of the optical system 10 to be able to amplify
optical signals in two ways, and transmit them. The repeating
station 30 also has a function of controlling the optical level, a
function of detecting cut of the optical cable, and a function of
automatic restoration after the cut is detected, between repeaters
and between repeater stations. The repeating station 30 comprises
an optical amplifier which can remotely pump, as will be described
later.
[0085] The receiving station 40 is a transmission terminal station
which transmits/receives optical signals. The receiving station 40
comprises an optical transmitting means 42, a level monitoring
means 43, an optical coupler 51, a loopback light detecting means
44, a controlling means (control unit) 45 and an optical receiving
means 41.
[0086] The optical transmitting means 42 multiplexes third
reception light (.lambda.1R) and second pumping light (.lambda.3PR)
amplifying the third reception light (.lambda.1R) and amplifies
them, then outputs the amplified optical signal to an internal
optical fiber. The optical transmitting means 42 comprises a
transmitting unit 42a, a second pumping source (pumping source 2)
42d, an optical amplifier 42b and an isolator 42c.
[0087] The transmitting unit 42a is similar to the above
transmitting unit 22a. The second pumping source 42d generates the
second pumping light (.lambda.3R). The optical amplifier 42b
amplifies an optical signal, an EDFA being used for it. The
isolator 42c sends an optical signal inputted from the optical
amplifier 42b to the optical coupler 51, and absorbs power of the
optical signal leaking from the optical coupler 51.
[0088] The optical signal outputted from the transmitting unit 42a
and the second pumping light (.lambda.3PR) from the second pumping
source 42d are optically amplified by the optical amplifier 42b,
and the optically amplified optical signal is sent to the optical
coupler 51 via the isolator 42c.
[0089] The level monitoring means 43 is connected to the optical
transmitting means 41 to detect a level of the optical signal
outputted from the optical transmitting means 41, which comprises a
fourth filter (filter 4) 43a and a third optical detector
(photodiode 3) 43b. The fourth filter 43a extracts only a
.lambda.1R component in the optical signal (.lambda.1R+.lambda.3PR)
outputted from the optical amplifier 42b and outputs it, an optical
filter, for example, being used for it. The third optical detector
43b detects an output from the fourth filter 43a, a photodiode, for
example, being used for it.
[0090] The optical coupler 51 is connected to the internal optical
fiber to transmit an optical signal in the internal optical fiber
to a second optical fiber connected to the repeating station 30.
The optical coupler 51 can also receive an optical signal having a
predetermined wavelength in an optical signal transmitted from the
repeating station 30 through the second optical fiber, and branch
the optical signal in a plurality of directions and output it, an
optical fiber of a fusion type with 1.times.3 terminals (not shown)
being used for it. The second optical fiber signifies an optical
fiber transmitting optical signals send from the receiving
station's side. Hereinafter, the above first optical fiber and this
second optical fiber will be used in the similar meanings.
[0091] The loopback light detecting means 44 is connected to the
optical coupler 51 to receive a optical monitoring signal
(.lambda.3PR') transmitted from the repeating station 30. The
loopback light detecting means 44 comprises a sixth filter (filter
6) 44a, a fourth optical detector (photodiode 4) 44b. The sixth
filter 44a extracts only the (.lambda.3PR') component in an optical
signal (.lambda.1L'+.lambda.2PL'+.- lambda.3PR') from the repeating
station 30 outputted from the optical coupler 51 and outputs it, a
function of which is realized by, for example, an optical filter.
The fourth optical detector 44b detects an output from the sixth
filter 44a, a function of which is realized by, for example, a
photodiode.
[0092] The controlling means 45 is connected to the optical
receiving means 41, the level monitoring means 43 and the loopback
light detecting means 44 to control the output level of second
pumping light (.lambda.3PR) on the basis of a reception level of
the optical monitoring signal (.lambda.3PR') from the loopback
light detecting means 44. Each of the controlling means 45 and the
controlling means 25 (in the transmitting station 20) has a
disconnect detecting function to be able to detect occurrence of a
fault in the second optical fiber. This will be explained in a
second modification of the first embodiment to be described
later.
[0093] Only the .lambda.3PR component in the optical signal
outputted from the optical transmitting means 42 is extracted by
the fourth filter 43a, an output from the fourth filter 43a is
detected by the third optical detector 43b, the optical monitoring
signal (.lambda.3PR') transmitted from the repeating station 30 is
received by the loopback light detecting means 44, the .lambda.3PR
component and the .lambda.3PR' component are inputted to the
controlling means 45, and the output level of the second pumping
light (.lambda.3PR) is controlled by the controlling means 45 on
the basis of the reception levels of these, and adjusted to the
optimum output power.
[0094] The optical receiving means 41 is connected to the optical
coupler 51 to receive an optical signal from the repeating station
30, which comprises a third filter (filter 3) 41a and a receiving
unit 41b. The third filter 41a extracts only a .lambda.1L'
component in the optical signal inputted from the optical coupler
51. The receiving unit 41 is similar to the above receiving unit
21. The receiving unit 41 receives an optical signal having the
.lambda.1L' component from the third filter 41a, electro-optically
convert it, and sends a voice signal or a data signal on the
telephone to another network (not shown).
[0095] In FIG. 1, wavelengths of optical signals used between the
receiving station 40 and the repeating station 30 are as follows.
Namely, kinds of wavelengths of optical signals sent from the
repeating station 30 to the receiving station 40 are three
(.lambda.1L', .lambda.2PL' and .lambda.3PR'). Kinds of wavelengths
of optical signals (transmission light) sent from the receiving
station 40 to the repeating station 30 are two (.lambda.1R and
.lambda.3PR).
[0096] In the wavelengths of transmission light from the receiving
station 40 to the repeating station 30, .lambda.1R is a wavelength
of an optical signal having a component on which a signal component
has been superimposed. .lambda.3PR is a wavelength of the second
pumping source 42d. In the wavelengths of transmission light from
the repeating station 30 to the receiving station 40, .lambda.1L'
is a wavelength of an optical signal having a component on which a
signal component has been superimposed. .lambda.2PL' and
.lambda.3PR' are wavelengths of two kinds of pumping sources in the
repeating station 30. Optical signals having these wavelengths
become monitor light, and are inputted to the receiving station
40.
[0097] FIG. 2 is a diagram showing an internal structure of the
repeating station 30 according to the first embodiment of this
invention. On the right side of this drawing is the receiving
station 40 (B station). On the left side is the transmitting
station 20 (A station). The repeating station 30 shown in FIG. 2
comprises a first optical transmitting means 31, a first loopback
means 32, a second optical transmitting means 33, a second loopback
means 34, and four optical couplers 50.
[0098] The first optical transmitting means 31 receives the first
transmission light (.lambda.1L) and the first pumping light
(.lambda.2PL) transmitted from the transmitting station 20 through
the first optical fiber, amplifies the first transmission light
(.lambda.1L) and the first pumping light (.lambda.2PL), and
transmits second transmission light (.lambda.1L') and second
pumping light (.lambda.2PL') to the second optical fiber toward the
receiving station 40. The first optical transmitting means 31
comprises a first optical amplifier (optical amplifier 1) 31a, a
third pumping source 31b, two optical couplers 50 and an isolator
31c.
[0099] The first optical amplifier 31a receives the first
transmission light (.lambda.1L) and the first pumping light
(.lambda.2PL), amplifies the first transmission light (.lambda.1L)
and the first pumping light (.lambda.2PL), and outputs them. The
third pumping source 31b generates the pumping light
(.lambda.2PL').
[0100] Each of the two optical couplers 50 multiplexes optical
signals in two directions, a function of which is realized by, for
example, an optical fiber of a fusion type with 1.times.2 terminals
(not shown). An optical signal is inputted from one terminal, and
the optical signal is outputted as the same optical signals from
two terminals. On the other hand, optical signals are inputted from
the two terminals, and the optical signals are outputted as the
same optical signal from the one terminal.
[0101] Accordingly, these optical couplers 50 can multiplex and
demultiplex optical signals. An optical signal from the
transmitting station 20 is fed through the optical couplers 50 in
two stages provided on the entrance's side, multiplexed with
.lambda.2PL' from the third pumping source 31b by the optical
coupler 50 in the third stage at the input of the first optical
amplifier 31a, and inputted to the first optical amplifier 31a. The
optical signal amplified by the first optical amplifier 31a is
demultiplexed into two directions by the optical coupler 50.
[0102] The amplified optical signal from the first optical
amplifier 31a is split by the optical coupler 50 connected to the
output's side of the first optical amplifier 31a, an optical signal
having a wavelength .lambda.1L' is sent toward the output isolator
31c (toward the receiving station 40), and an optical signal having
wavelengths .lambda.1L' and .lambda.2PL' is sent to the input's
side (toward the transmitting station 20). Incidentally, such an
optical signal containing two kinds of wavelengths will be
occasionally referred as an optical signal of
.lambda.1L'+.lambda.2PL' in the following descriptions.
Additionally, the wavelength .lambda.1L' component will be
abbreviated as .lambda.1L', occasionally.
[0103] The isolator 31c sends the split optical signal to the
optical coupler 50. The isolator 31c also absorbs power of the
optical signal leaking from the optical coupler 50 to prevent the
optical signal from flowing into the first optical amplifier
31a.
[0104] On the output's side of the isolator 31c provided is the
optical coupler 50. Namely, the optical coupler 50 is provided on
the output's side of the first optical transmitting means 31 to
output second transmission light (.lambda.1L') and second pumping
light (.lambda.2PL') to the optical receiving apparatus's side, and
outputs the third transmission light (.lambda.1R) and the third
pumping light (.lambda.3PR) from the optical receiving apparatus's
side, which functions as a first optical coupler.
[0105] The first loopback means 32 is connected to the first
optical transmitting means 31 to extract the second pumping light
(.lambda.2PL') from the optical signal amplified by the first
optical transmitting means 31, and outputs the second pumping light
(.lambda.2PL'), which comprises a first loopback filter (filter 1)
32b and an isolator 32a. The first loopback filter 32b is inputted
thereto an optical signal (.lambda.1L'+.lambda.2PL') outputted from
the above first optical transmitting means 31, attenuates
.lambda.1L' in these wavelengths, and outputs the remaining
wavelength .lambda.2PL'. The isolator 32a has the similar function
to the above isolator 31c. In concrete, the isolator 32a is
provided in order to prevent an optical signal containing an
unnecessary component for the first loopback filter 32b from
flowing back.
[0106] The second optical transmitting means 33 receives the third
transmission light (.lambda.1R) and the third pumping light
(.lambda.3PR) transmitted from the receiving station 40 through the
second optical fiber, amplifies the light, and outputs fourth
transmission light (.lambda.1R'). The second optical transmitting
means 33 comprises a second optical amplifier (optical amplifier 2)
33c, a fourth pumping source 33b, two optical couplers 50 and an
isolator 33a. The fourth pumping source 33b generates fourth
pumping light (.lambda.1R'). Incidentally, the second optical
amplifier 33c and the isolator 33a are similar to the first optical
amplifier 31a and the isolator 31c mentioned above, and the optical
coupler 50 is similar to that mentioned above, duplicated
descriptions of which are thus omitted.
[0107] On the output's side of the second optical transmitting
means 33 (on the output's side of the second optical amplifier 33c)
provided is an optical coupler 50 to output an optical signal from
the first loopback means 32 and an optical signal from the second
optical transmitting means 33 toward the transmitting station 20
(optical transmitting apparatus), and to output the first
transmission light (.lambda.1L) and the first pumping light
(.lambda.2PL) from the transmitting station 20. The optical coupler
50 functions as a second optical coupler.
[0108] The second loopback means 34 is connected to the second
optical amplifier 33c to extract fourth pumping light
(.lambda.3PR') from the optical signal amplified by the second
optical amplifier 33c, and outputs the fourth pumping light
(.lambda.3PR'). The second loopback means 34 comprises a second
loopback filter 34a (filter 2) and an isolator 34b. The second
loopback filter 34a is inputted thereto an optical signal having
wavelengths (.lambda.1R'+.lambda.3PR') outputted from the second
optical transmitting means 33, attenuates the .lambda.1R' component
in these wavelengths, and outputs the remaining .lambda.3PR'
component. The isolator 34b has a function similar to the above
isolator 31c. In concrete, the isolator 34b is installed in order
to prevent an optical signal having an unnecessary component for
the second loopback filter 34a from flowing back.
[0109] Each of the transmitting station 20 and the receiving
station 40 in FIG. 1 has these optical couplers 50, but denotation
of the optical couplers 50 is omitted. Similarly, these optical
couplers 50 provided in each of the transmitting station 20, the
repeating station 30 and the receiving station 40 are omitted in
the drawings in embodiments and modifications to be described
later.
[0110] In FIG. 2, an optical signal repeating operation of the
repeating station 30 is as follows. Namely, transmission light
(.lambda.1L +.lambda.2PL) from the transmitting station 20 is
inputted to the transmitting means 31, multiplexed with
.lambda.2PL' from the third pumping source 31b in the first optical
transmitting means 31, optically amplified by the first optical
amplifier 31a. After that, the repeater-amplified .lambda.1L'
component is outputted along with the residual pumping light
(.lambda.2PL') as amplified signal light (.lambda.1L'+.lambda.2PL')
to the remote receiving station 40 via the isolator 31c.
[0111] Transmission light (.lambda.1R+.lambda.3PR) from the
receiving station 40 is inputted to the second optical transmitting
means 33, multiplexed with .lambda.1R' from the fourth pumping
source 33b in the second optical transmitting means 33, optically
amplified by the second optical amplifier 33c. The
repeater-amplified .lambda.1R' is outputted along with the residual
pumping light .lambda.3PR' as amplified signal light
(.lambda.1R'+.lambda.3PR') to the remote transmitting station 20
via the isolator 33a.
[0112] In FIG. 2, an optical signal looping-back operation from the
repeating station 30 to the transmitting station 20 is as follows.
Namely, an optical signal amplified by the first optical amplifier
31a is branched toward the first loopback filter 32b in the first
loopback means 32. The .lambda.1L' component of the light signal is
removed by the first loopback filter 32b, and the .lambda.2PL'
component is looped back to the transmitting station 20.
[0113] Similarly, an optical signal looping-back operation from the
repeating station 30 to the receiving station 40 as follows.
Namely, an optical signal amplified by the second optical amplifier
33c is branched toward the first loopback filter 32b in the second
loopback means 34. The .lambda.1R' component of the light signal is
removed by the first loopback filter 32b, and the .lambda.3PR'
component is looped back to the receiving station 40.
[0114] With the above structure, repeating and monitoring of the
light signal are performed among the transmitting station 20, the
repeating station 30 and the receiving station 40, optical
transmission using a remote pumping control is thereby
performed.
[0115] An electric signal such as a voice signal or the like on the
telephone is converted into an optical signal in the transmitting
station 20 (refer to FIG. 1), then transmission light
(.lambda.1L+.lambda.2PL) is transmitted from the transmitting
station 20. In the repeating station 30, transmission light
(.lambda.1L'+.lambda.2PL') and monitor light .lambda.3PR' are
transmitted in the above repeating operation to the receiving
station 40. In the receiving station 40, signal light .lambda.1L'
is extracted, converted into an electric signal, returned to a
signal for the telephone, and sent to another switching station or
the like.
[0116] On the other hand, amplified pumping light .lambda.2PL' to
be sent back from the repeating station 30 to the transmitting
station 20 is inputted to the optical coupler 51 in the
transmitting station 20, and branched into three directions; toward
the receiving unit 21a, the transmitting unit 22a and the loopback
light detecting means 24. For the receiving unit 21a and the
transmitting unit 22a among them, .lambda.2PL' is a noise
component, thus removed by the first filter 21b and the isolator
22c. .lambda.2PL' is inputted to the second optical detector 24b in
the loopback light detecting means 24. In the control unit 25, an
actual transmission loss between the transmitting station 20 and
the repeating station 30 is calculated on the basis of a difference
between a level of the first optical detector 23b and a level of
the second optical detector 24b, and an output level of the first
pumping source 22d is so controlled as to yield the optimum
amplification factor.
[0117] Similarly, an electric signal such as a telephone signal or
the like from the receiving station 40 is converted into an optical
signal. Transmission light (.lambda.1R+.lambda.3PR) is transmitted
from the receiving station 40. In the repeating station 30,
transmission light (.lambda.1R'+.lambda.3PR') and monitor light
.lambda.2PL' are transmitted in the above repeating operation to
the transmitting station 20. In the transmitting station 20, signal
light .lambda.1R' is extracted, converted into an electric signal,
returned to a signal for the telephone, and sent to another
switching station or the like.
[0118] On the other hand, amplified pumping light .lambda.3PR' to
be sent back from the repeating station 30 to the receiving station
40 is inputted to the optical coupler 51 in the receiving station
40, then branched into three directions; toward the receiving unit
41a, the transmitting unit 42a and the loopback light detecting
means 44. For the receiving unit 41a and the transmitting unit 42a
among them, .lambda.3PR' is a noise component, thus removed by the
third filter 41a and the isolator 42c. .lambda.3PR' is inputted to
the fourth optical detector 44b (photodiode 4) in the loopback
light detecting means 44. In the control unit 45, an actual
transmission loss between the receiving station 40 and the
repeating station 30 is calculated on the basis of a difference
between a level of the third optical detector 43b and a level of
the fourth optical detector 44b, and the output level of the second
pumping source 42d is so controlled as to yield the optimum
amplification factor.
[0119] As this, communication is performed among the transmitting
station 20, the repeating station 30 and the receiving station 40
using only optical cables in one system, and the output level of
the pumping source is automatically controlled in each of the
transmitting station 20, the repeating station 30 and the receiving
station 40, so that the optimum communication becomes possible.
[0120] By introducing this optical system 10 as above, the
installation cost and maintenance cost of the optical cables are
largely decreased, and reliability and safety of this optical
system 10 is remarkably improved.
[0121] (A1) Description of First Modification of First Embodiment
of the Invention
[0122] FIG. 3 is a diagram showing a structure of an optical system
according to a first modification of the first embodiment of this
invention. An optical system 10c shown in FIG. 3 is a system in
which transmission light, reception light and pumping light can be
transmitted/received through optical cables in one system. The
optical system 10c comprises a transmitting station (A station)
20c, a first repeating station (repeater 1) 30c, a second repeating
station (repeater 2) 30c' and a receiving station (B station) 40c,
where the stations are connected by optical cables, whereby optical
signals are transmitted/received in two ways.
[0123] In FIG. 3, a wavelength of transmission light of the
transmitting station 20c is .lambda.1L, and a wavelength of a first
pumping source 22d is .lambda.2PL. A wavelength of the receiving
station 40c is .lambda.1R, and a wavelength of a second pumping
source 42d is .lambda.3PR.
[0124] In FIG. 3, parts designated by like reference characters
have like or corresponding functions described above, further
descriptions of which are thus omitted. Hereinafter, only parts
differing from those in the first embodiment will be described. In
other embodiments and modifications, modified modes of the
transmitting station 20, the repeating station 30 and the receiving
station 40 of the optical system will be described.
[0125] FIG. 4 is a diagram showing an internal structure of a first
repeating station according to the first modification of the first
embodiment of this invention. The first repeating station 30c shown
in FIG. 4 comprises a first optical transmitting means 62, a second
optical transmitting means 63, and two optical couplers 50 (not
shown).
[0126] The first optical transmitting means 62 receives first
transmission light (.lambda.1L) and first pumping light
(.lambda.2PL) transmitted from a transmitting station 20c through a
first optical fiber, changes either a level of the first
transmission light (.lambda.1L) or a level of the first pumping
light (.lambda.2PL) to a necessary level, amplifies the changed
first transmission light (.lambda.1L) and first pumping light
(.lambda.2PL), and outputs second transmission light (.lambda.1L')
and second pumping light (.lambda.2PL'). The first optical
transmitting means 62 comprises a first pumping light adjusting
means 38, a first optical amplifier 31a, a pumping source 31b and
an isolator 31c.
[0127] The first pumping light adjusting means 38 splits the first
transmission light (.lambda.1L) and the first pumping light
(.lambda.2PL), attenuates a level of the pumping light
(.lambda.2PL) by a necessary level, and outputs the first
transmission light (.lambda.1L) and the first pumping light
(.lambda.2PL). The first pumping light adjusting means 38 comprises
a demultiplexer 38a, a variable attenuator (attenuator) 38b and an
optical coupler (not shown). The demultiplexer 38a splits into the
first transmission light (.lambda.1L) and the first pumping light
(.lambda.2PL), and outputs them, a function of which is realized by
an optical fiber of a fusion type. The variable attenuator 38b
attenuates an optical signal by a predetermined level, and outputs
it.
[0128] The second optical transmitting means 63 receives third
transmission light (.lambda.1R) and third pumping light
(.lambda.3PR) transmitted from a receiving station 40c through a
second optical fiber, changes either a level of the third
transmission light (.lambda.1R) or a level of the third pumping
light (.lambda.3PR) to a necessary level, amplifies the changed
third transmission light (.lambda.1R) and third pumping light
(.lambda.3PR), and outputs fourth transmission light (.lambda.1R')
The second optical transmitting means 63 comprises a second pumping
light adjusting means 39, a second optical amplifier 33c and an
isolator 33a.
[0129] The second pumping light adjusting means 39 splits into the
third transmission light (.lambda.1R) and the third pumping light
(.lambda.3PR), attenuates a level of the pumping light
(.lambda.3PR) by a necessary level, and outputs the third
transmission light (.lambda.1R) and the third pumping light
(.lambda.3PR). The second pumping light adjusting means 39
comprises a demultipexer 39a, a variable attenuator (attenuator)
39b, and an optical coupler 50 (not shown). The demultiplexer 39a
splits into the third transmission light (.lambda.1R) and the third
pumping light (.lambda.3PR), and outputs them, a function of which
is realized by an optical fiber of a fusion type. The variable
attenuator 39b attentuates an optical signal by a predetermined
level, and outputs it.
[0130] Further descriptions of parts in FIG. 4 corresponding to
those described above are omitted here.
[0131] Internal processing in the first repeating station 30c is as
follows. Namely, transmission light (.lambda.1L+.lambda.2PL) from
the transmitting station 20c is inputted to the first repeating
station 30c, split into two by the demultiplexer 38a of the first
pumping light adjusting means 38, and demultiplexed into a
.lambda.1L component and a .lambda.2pl component. The demultiplexed
.lambda.1L is inputted as it is to the first optical amplifier 31a
through the optical coupler 50 (not shown). A level of .lambda.2PL
is adjusted by the variable attenuator 38b. .lambda.2PL is then
multiplexed with the above .lambda.1L by the optical coupler 50,
inputted to the first optical amplifier 31a, then optically
amplified with residual pumping light .lambda.2PL, a level of which
has been adjusted, from the third pumping source 31b. The resulting
optical signal (.lambda.1L'+.lambda.2PL') is transmitted to the
isolator 31c, and sent to the second repeating station 30c'.
[0132] Inputted light (.lambda.1R'+.lambda.3PR') from the second
repeating station 30c' is repeater-amplified, and an optical signal
(.lambda.1R"+.lambda.3PR") is transmitted to the transmitting
station 20c.
[0133] Similarly, internal processing in the second repeating
station 30c' is as follows. Namely, transmission light
(.lambda.1L'+.lambda.2PL') from the first repeating station 30c is
inputted to the second repeating station 30c', split into two by
the demultiplexer 38a, and demultiplexed into a .lambda.1L'
component and a .lambda.2PL' component. The demultiplexed
.lambda.1L' is inputted as it is to the first optical amplifier 31a
through the optical coupler 50. A level of .lambda.2PL' is adjusted
by the variable attenuator 38b. .lambda.2PL' is multiplexed with
.lambda.1L' by the optical coupler 50, and inputted to the first
optical amplifier 31a, optically amplified with residual pumping
light (.lambda.2PL'), a level of which has been adjusted, from the
third pumping source 31b by the first optical amplifier 31a. The
resulting optical signal (.lambda.1L'"+.lambda.2PL") is transmitted
to the isolator 31c, and sent to the receiving station 40c.
[0134] Inputted light (.lambda.1R+.lambda.3PR) from the receiving
station 40c is processed in the similar manner, and a light signal
(.lambda.1R'+.lambda.3PR') is transmitted to the first repeating
station 30c.
[0135] With the above structure, repeating and monitoring of the
optical signals are performed among the transmitting station 20c,
the first repeating station 30c, the second repeating station 30c'
and the receiving station 40c, optical transmission using a remote
pumping control is thereby performed.
[0136] In FIG. 3, the transmission light .lambda.1L from the
transmitting station 20c is multiplexed with the pumping source
.lambda.2PL, optically amplified by the optical amplifier 22b, then
transmitted along with residual pumping light to the first
repeating station 30c via the optical coupler 51. From the first
repeating station 30c, amplified transmission light .lambda.1L' and
amplified pumping light .lambda.2PL' are sent to the second
repeating station 30c'.
[0137] In the second repeating station 30c', reception light
(.lambda.1L'+.lambda.2PL') from the first repeating station 30c is
amplified, and amplified transmission light .lambda.1L" and
amplified pumping light .lambda.2PL" are sent to the receiving
station 40c. A flow of transmission light from the receiving
station 40c to the transmitting station 20c is similar.
[0138] In each of the stations, the administrator, for example,
adjusts attenuation quantities of the variable attenuators 38b and
39b on the basis of level values of the light, whereby appropriate
quantities of light are outputted.
[0139] As this, communication is performed among the transmitting
station 20c, the first repeating station 30c, the second repeating
station 30c' and the receiving station 40c using only optical
cables in one system, and the output level of the pumping source is
automatically adjusted in each of the stations, which allows the
optimum communication.
[0140] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and the optical cables are
monitored with pumping light and residual pumping light, which
allows large improvement of reliability and safety of this optical
system 10c.
[0141] (A2) Description of Second Modification of First Embodiment
of the Invention
[0142] Further, it is possible to improve the reliability of the
system by detecting disconnection of optical signals in the
transmission terminal station.
[0143] FIG. 5 is a diagram showing a structure of an optical system
according to a second modification of the first embodiment of this
invention. An optical system 10a shown in FIG. 5 is a system in
which transmission light, reception light and pumping light can be
transmitted/received through optical fiber cables in one system.
The optical system 10a comprises a transmitting station (A station)
20a, a repeating station (repeater) 30a and a receiving station (B
station) 40a, where the stations are connected by optical cables,
and optical signals are transmitted/received in two ways.
[0144] In FIG. 5, a wavelength of transmission light of the
transmitting station 20a is .lambda.1L, a wavelength of a first
pumping source 22d is .lambda.2PL, a wavelength of transmission
light of the receiving station 40a is .lambda.1R, a wavelength of a
second pumping source 42d is .lambda.3PR.
[0145] The transmitting station 20a comprises a disconnect
detecting means 26 which detects that a fault occurs in the first
optical fiber. The disconnect detecting means 26 comprises a first
transmitting side filter (filter 7) 26a, a first transmitting side
monitoring means (photodiode 5) 26b, and a first transmitting side
disconnect detection outputting means (disconnect detection)
26c.
[0146] The first transmitting side filter 26a extracts residual
pumping light (.lambda.3PR') from a received optical signal, and
outputs it, a function of which is realized by an optical filter.
The first transmitting side monitoring means 26b detects the
residual pumping light (.lambda.3PR') from the first transmitting
side filter 26a, a function of which is realized by a photodiode.
The first transmitting side disconnect detection outputting means
26c monitors the operation of the first transmitting side
monitoring means 26b, and outputs information relating to
presence/absence of the residual pumping light (.lambda.3PR'), a
function of which is realized by directly displaying it by
instruments or the like.
[0147] In the transmitting station 20a, the first transmitting side
filter 26a extracts the residual pumping light (.lambda.3PR') from
a received optical signal, the first transmitting side monitoring
means 26b detects the residual pumping light (.lambda.3PR') from
the first transmitting side filter 26a, the first transmitting side
disconnect detection outputting means 26c monitors the operation of
the first transmitting side monitoring means 26b and outputs
information relating to presence/absence of the residual pumping
light (.lambda.3PR').
[0148] The receiving station 40a comprises a disconnect detecting
means 46 which detects that a fault occurs in the first optical
fiber. The disconnect detecting means 46 comprises a first
receiving side filter (filter 8) 46a, a first receiving side
monitoring means (photodiode 6) 46b, and a first receiving side
disconnect detection outputting means (disconnect detection)
46c.
[0149] The first receiving side filter 46a extracts residual
pumping light (.lambda.2PL') from a received optical signal, and
outputs it, a function of which is realized by an optical filter.
The first receiving side monitoring means 46b detects the residual
pumping light (.lambda.2PL') from the first receiving side filter
46a, a function of which is realized by a photodiode. The first
receiving side disconnect detection outputting means 46c monitors
the operation of the first receiving side monitoring means 46b, and
outputs information relating to presence/absence of the residual
pumping light (.lambda.2PL'), a function of which is realized by
directly displaying it by instruments or the like.
[0150] In the receiving station 40a, the first receiving side
filter 46a extracts residual pumping light (.lambda.2PL') from a
received optical signal, the first receiving side monitoring means
46b detects the residual pumping light (.lambda.2PL') from the
first receiving side filter 46a, and the first receiving side
disconnect detection outputting means 46c monitors the operation of
the first receiving side monitoring means 46b and outputs
information relating to presence/absence of the residual pumping
light (.lambda.2PL').
[0151] In FIG. 5, parts designated by like reference characters
have like or corresponding functions described above, further
descriptions of which are thus omitted. Hereinafter, only parts
differing from those in the first embodiment will be described.
[0152] FIG. 6 is a diagram showing an internal structure of the
first repeating station according to the second modification of the
first embodiment of this invention. The first repeating station 30a
shown in FIG. 6 comprises a first disconnect detecting means 35 and
a second disconnect detecting means 36. The first disconnect
detecting means 35 is disposed at the entrance of the first optical
fiber to detect cut of the first optical fiber. The first
disconnect detecting means 35 comprises a third filter (filter 3)
35a, a first optical detector (photodiode 1) 35b and a first
disconnect detection outputting means (disconnect detection)
35c.
[0153] The third filter 35a extracts residual pumping light
(.lambda.3PR') from a received optical signal, and outputs it. The
first optical detector 35b detects the residual pumping light
(.lambda.3PR') from the third filter 35a. The first disconnect
detection outputting means 35c monitors the operation of the first
optical detector 35b, and outputs information relating to
presence/absence of the residual pumping light (.lambda.3PR').
[0154] The second disconnect detecting means 36 is disposed at the
entrance of the second optical fiber to detect cut of the second
optical fiber. The second disconnect detecting means 36 comprises a
fourth filter (filter 4) 36a, a second optical detector (photodiode
2) 36b, and a second disconnect detection outputting means
(disconnect detection) 36c.
[0155] The fourth filter 36a extracts residual pumping light
(.lambda.2PL') from a received optical signal, and outputs it. The
second optical detector 36b detects the residual pumping light
(.lambda.2PL') from the fourth filter 36a. The second disconnect
detection outputting means 36c monitors the operation of the second
optical detector 36b, and outputs information relating to
presence/absence of the residual pumping light (.lambda.2PL').
[0156] With the above structure, in the normal state, the first
transmitting side disconnect detection outputting means 26c keep
receiving .lambda.3PR' so that only .lambda.3PR' can pass through
the first transmitting side filter 26a in the transmitting station
20a (refer to FIG. 5).
[0157] When cut of the optical cable occurs, the optical signal is
reflected by an end of the optical cable having been cut, and
transmits in the opposite direction. When optical power loss (loss)
is large at the end of the optical cable having been cut, returned
light is not detected. This non-detection is detected by the
monitoring function. When the optical power loss is small,
transmission light from the transmitting station 20a is returned to
the transmitting station 20a, the return is not detected, so that
no alarm generates. When cut of the optical cable occurs, its input
dies out. For this, when cut of the optical cable is detected by
the disconnect detection, an alarm generates.
[0158] In concrete, when cut of the optical cable occurs between
the repeating station 30a and the transmitting station 20a,
.lambda.1R'+.lambda.2PL'+.lambda.3PR' components generate in an
optical signal inputted from the transmitting station 20a to the
repeating station 30a. Accordingly, .lambda.3PR' that is never
inputted from the transmitting station 20a in the normal state is
detected, whereby cut of the optical cable can be detected.
[0159] Similarly, in the receiving station 40a, cable cut is
detected by allowing only .lambda.2PL' to pass through the first
receiving side filter 46a.
[0160] As this, communication is performed among the transmitting
station 20a, the repeating station 30a and the receiving station
40a using only the optical cables in one system, and the output
level of the pumping source is automatically controlled in each of
the stations, which allows the optimum communication.
[0161] The installation cost and maintenance cost of the optical
cables are largely decreased, and the reliability and safety of
this optical system 10a are remarkably improved since each of the
stations can detect cut of the optical cable.
[0162] (A3) Description of Third Modification of First Embodiment
of the Invention
[0163] Disconnect detection in the case where a plurality (not less
than three) of repeating stations are connected is performed in the
similar manner. FIG. 7 is a diagram showing a structure of an
optical system according to a third modification of the first
embodiment of this invention. An optical system 10b shown in FIG. 7
is a system in which transmission light, reception light and
pumping light can be transmitted/received through optical fibers in
one system. The optical system 10b comprises a transmitting station
(A station) 20b, a first repeating station (repeater 1) 30b, a
second repeating station (repeater 2) 30b' and a receiving station
(B station) 40b, where the stations are connected by optical cables
to transmit/receive optical signals in two ways.
[0164] The transmitting station 20b is a transmission terminal
station transmitting/receiving optical signals, which comprises an
optical receiving means 21, an optical transmitting means 22, a
disconnect detecting means 26 and an optical coupler 51. The
receiving station 40b is a transmission terminal station
transmitting/receiving optical signals, which comprises an optical
receiving means 41, an optical transmitting means 42, a disconnect
detecting means 46 and an optical coupler 51. These have like or
corresponding functions to those described above, further
descriptions of which are thus omitted.
[0165] In FIG. 7, a wavelength of transmission light of the
transmitting station 20b is .lambda.1L, a wavelength of a first
pumping source 22d is .lambda.2PL, a wavelength of transmission
light of the receiving station 40b is .lambda.1R, and a wavelength
of a second pumping source 42d is .lambda.3PR. Transmission light
.lambda.1L from the transmitting station 20 is multiplexed with the
pumping source .lambda.2PL by an optical coupler 50, optically
amplified by a first optical amplifier 31a, then transmitted along
with residual pumping light to the repeating station 30 via the
optical coupler 51.
[0166] Transmission of an optical signal from the transmitting
station 20b to the receiving station 40b is as follows. Namely,
transmission light (.lambda.1L+.lambda.2PL) from the transmitting
station 20b is inputted to the first repeating station 30b, and
optically amplified in the first repeating station 30b. An optical
signal (.lambda.1L'+.lambda.2PL') is sent to the second repeating
station 30b', and again optically amplified in the second repeating
station 30b'. An optical signal (.lambda.1L"+.lambda.2PL") is then
sent to the receiving station 40b.
[0167] On the other hand, transmission of an optical signal from
the receiving station 40b to the transmitting station 20b is as
follows. Namely, transmission light (.lambda.1R+.lambda.3PR) from
the receiving station 40b is inputted to the second repeating
station 30b', and optically amplified in the second repeating
station 30b'. An optical signal (.lambda.1R'+.lambda.3PR') is then
sent to the first repeating station 30b, and again optically
amplified in the first repeating station 30b. An optical signal
(.lambda.1R"+.lambda.3PR") is sent to the transmitting station
20b.
[0168] FIG. 8 is a diagram showing a structure of the first
repeating station 30b according to the third modification of the
first embodiment of this invention. The first repeating station 30b
shown in FIG. 8 comprises a first optical transmitting means 61, a
first disconnect detecting means 37, a second optical transmitting
means 63 and a second disconnect detecting means 67.
[0169] The first optical transmitting means 61 receives the first
transmission light (.lambda.1L) and the first pumping light
(.lambda.2PL) transmitted from the transmitting station 20b through
the first optical fiber, amplifies the first transmission light
(.lambda.1L) and the first pumping light (.lambda.2PL), and outputs
second transmission light (.lambda.1L') and second pumping light
(.lambda.2PL'). The first optical transmitting means 61 comprises a
first optical amplifier 31a, a first filter (filter 1) 31d, and an
isolator 31c. Unlike the above first optical transmitting means 31,
the first optical transmitting means 61 has the first filter 31d at
the input of the first optical amplifier 31a. The first filter 31d
extracts (.lambda.1L+.lambda.2PL') components from a received
optical signal, and outputs them.
[0170] The first disconnect detecting means 37 monitors an output
from the first optical amplifier 31a, and outputs information
relating to presence/absence of (.lambda.1L'+.lambda.2PL')
components in the transmission light. The first disconnect
detecting means 37 comprises a second filter (filter 2) 37a
extracting .lambda.2PL', a first optical detector (photodiode 1)
37b detecting a level of outputted light from the second filter
37a, and a first disconnect detection outputting means (disconnect
detection) 37c. Unlike the above first disconnect detecting means
35, the first disconnect detecting means 37 is directly connected
to the output of the first optical amplifier 31a.
[0171] Similarly, the second optical transmitting means 63 receives
third transmission light (.lambda.1R') and residual pumping light
(.lambda.3PR') transmitted from the second repeating station 30b',
amplifies the third transmission light (.lambda.1R') and the
residual pumping light (.lambda.3PR'), and outputs transmission
light (.lambda.1R"+.lambda.3PR"). The second optical transmitting
means 63 comprises a second optical amplifier 33c, a third filter
(filter 3) 33d, and an isolator 33a. Unlike the above second
optical transmitting means 33, the second optical transmitting
means 63 has the third filter 33d at the input of the second
optical amplifier 33c. The third filter 33d extracts transmission
light components (.lambda.1R'+.lambda.3PR') from a receiving
optical signal, and outputs them.
[0172] The second disconnect detecting means 67 monitors an output
of the second optical amplifier 33c, and outputs information
relating to presence/absence of the transmission light components
(.lambda.1R'+.lambda.3PR'). The second disconnect detecting means
67 comprises a fourth filter (filter 4) 67a extracting
.lambda.3PR', a second optical detector (photodiode 2) 67b
detecting a level of outputted light from the fourth filter 67a,
and a second disconnect detection outputting means (disconnect
detection) 67c. Unlike the above second disconnect detecting means
35, the second disconnect detecting means 67 is directly connected
to the output of the second optical amplifier 33c.
[0173] Meanwhile, parts designated by like reference characters
have like or corresponding functions described above, further
descriptions of which are thus omitted.
[0174] With this structure, disconnect detection is performed. In
the (.lambda.1L+.lambda.2PL) components inputted to the first
repeating station 30b, only (.lambda.1L+.lambda.2PL) components are
inputted to the first optical amplifier 31a, and optically
amplified. (.lambda.1L'+.lambda.2PL') components optically
amplified with residual pumping light (not shown) are transmitted
to the second repeating station 30b' (refer to FIG. 7) via the
isolator 31c.
[0175] Only a .lambda.2PL' component in the
(.lambda.1L'+.lambda.2PL') components is left by the second filter
37a, optical detection is performed in the first optical detector
37b, and the .lambda.2PL' component is detected by the first
disconnect detecting means 37c.
[0176] Flow of an optical signal from the second repeating station
30b' is similar.
[0177] When cut of the optical cable occurs between the
transmitting station 20b and the first repeating station 30b,
inputs of .lambda.2PL' to the first optical detector 37b die out,
thus an alarm generates. When cut of the optical cable occurs
between the first repeating station 30b and the second repeating
station 30b', inputs of the .lambda.3PR' component to the second
optical detector 67b die out, thus an alarm generates.
[0178] The first optical detector 37b and the second optical
detector 67b keep detecting pumping light of the opposite stations
at any time. When any part of the optical cable is cut between the
transmitting station 20b and the receiving station 40b, pumping
light of the opposite station comes not to be received. When the
inputs die out, an alarm generates, the cut is thereby
detected.
[0179] As this, communication is performed among the stations using
only the optical cables in one system, and the output level of the
pumping source is automatically controlled in each of the stations,
which allows the optimum communication.
[0180] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and reliability and safety of
this optical system 10b are remarkably improved since each of the
stations can detect cut of the optical cable.
[0181] (A4) Description of Fourth Modification of First Embodiment
of the Invention
[0182] A mode of transmission among a plurality of repeating
stations is possible in this modification, as well. FIG. 9 is a
diagram showing a structure of an optical system according to a
fourth modification of the first embodiment of this invention. When
an optical system 10d shown in FIG. 9 is compared with the above
optical system 10a shown in FIG. 5, a transmitting station 20d has
neither the level monitoring means 23 nor the disconnect detecting
means 26 of the transmitting station 20a (refer to FIG. 5), but has
a displaying unit 53a. A receiving station 40d has neither the
level monitoring means 43 nor the cut means 46 of the receiving
station 40a (refer to FIG. 5), but has a displaying unit 53b. These
displaying units 53a and 53b are connected to controlling means 25
and 45, respectively, to display desired values. A function of each
of these displaying unit 53a and 53b is realized by a display
apparatus, for example. Parts designated by like reference
character have like or corresponding functions described above,
further descriptions of which are thus omitted.
[0183] First, an operation of the controlling means 25 in the
transmitting station 20d is described. The controlling operation is
as in (p1) to (p5) below.
[0184] (p1) The controlling means 25 calculates a .lambda.2PL level
outputted from the transmitting station 20d, and stores it. (p2) A
.lambda.2PL' level of looped back light from a first repeating
station 30d is monitored by a second optical detector (photodiode
2) 24b.
[0185] (p3) An actual transmission loss between the transmitting
station 20d and the first repeating station 30d is calculated and
stored, and this result is displayed by the displaying unit
53a.
[0186] (p4) An optical output level of .lambda.2PL' at the first
repeating station 30d is calculated, and displayed.
[0187] (p5) Gain control is performed on a first pumping source 22d
so that the optimum optical level is inputted to the first
repeating station 30d.
[0188] A calculating method for this is as follows. Namely, an
actual transmission loss (dB) between the transmitting station 20d
and the first repeating station 30d is determined from the equation
(1):
L=(O+A-I)/2 (1)
[0189] Where, O (ou) is a .lambda.2PL optical output level (dBm), I
(ai) is a monitor light optical level (dBm) at the second optical
detector 22d, AIN is a .lambda.2PL optical input level (dBm)
inputted to a first optical amplifier 31a (refer to FIG. 10 to be
described later) of the first repeating station 30d, and A is an
optical amplification factor (dB) to the optical input level. Here,
dBm is a power ratio to one milliwatt.
[0190] When a relationship of O-L=AIN is substituted into the
equation (1), a relational equation between A and AIN becomes
equation (2):
O+I=A +2AIN (2)
[0191] A relationship between A and AIN is uniquely determined on
the basis of characteristics of the first optical amplifier 31a.
For this, once O and I can be obtained by turning its
characteristics into a database and preparing it by the
transmitting station 20d, it is possible to determine values of A
and AIN, thus L can be calculated. Incidentally, the relationship
between A and AIN is an input-output relationship of the first
optical amplifier 31a, so that the optical amplification factor AIN
at that time can be determined once the input level is known. From
a result of this calculation, it is possible to calculate an actual
transmission loss L (dB), and a .lambda.2PL' optical level
value=AIN+A (dBm).
[0192] Next, an operation of a controlling means 45 in the
receiving station 40d is as in (p6) to (p10) below:
[0193] (p6) The controlling means 45 calculates a .lambda.3PR
optical output level outputted from the optical amplifier 42b, and
stores it.
[0194] (p7) Returned light .lambda.3PR' from the second repeating
station 30d' is monitored by a fourth optical detector (photodiode
4) 44b.
[0195] (p8) An actual transmission loss between the receiving
station 40d and a second repeating station 30d' is calculated and
stored, then a result of this is displayed.
[0196] (p9) An optical output level of .lambda.3PR' at the second
repeating station 30d' is calculated, and displayed.
[0197] (p10) Gain control is performed on a second pumping source
42d so that the optimum optical level is inputted to the second
repeating station 30d'.
[0198] A calculating method for this is similar to that in the
description of the controlling means 25 of the transmitting station
20d. A control in the first repeating station 30d will be next
described with reference to FIG. 10. FIG. 10 is a diagram showing
an internal structure of the first repeating station 30d according
to the fourth modification of the first embodiment of this
invention. The first repeating station 30d shown in FIG. 10
comprises a second disconnect detecting means 64 and attenuation
control units 70a and 70a'.
[0199] The second disconnect detecting means 64 is disposed at an
entrance of a second optical fiber in order to detect a level of a
transmission optical signal, thereby detecting cut of the second
optical fiber. The second disconnect detecting means 64 comprises a
sixth filter (filter 6) 64a, and a second optical detector
(photodiode 2) 64b. Incidentally, the second disconnect detecting
means 64 is similar to the second disconnect detecting means 36
(refer to FIG. 6), but does not detect cut.
[0200] The sixth filter 64a is similar to the fourth filter 36a
(refer to FIG. 6), which extracts residual pumping light
(.lambda.2PL") from a transmission optical signal, and outputs it.
The second optical detector 64b is similar to the second optical
detector 36b (refer to FIG. 6), which detects a level of the
residual pumping light (.lambda.2PL") outputted from the sixth
filter 64a.
[0201] The attenuation control units 70a and 70a' control variable
attenators (attenuators) 38b and 39b, respectively. The
attentuation control unit 70a controls an attenuation quantity of
the first pumping light adjusting means on the basis of a
difference between a level detected by the second optical detector
64b and a level prepared beforehand.
[0202] At an entrance of the optical coupler 39a disposed is a
third filter (filter 3) 33d. The third filter 33d removes a
residual pumping light component (.lambda.2PL") from a received
optical signal. The others designated by like reference characters
have like or corresponding functions described above, further
descriptions of which are thus omitted.
[0203] In the first repeating station 30d, a control as follows is
performed. When transmission light (.lambda.1L+.lambda.2PL) from
the transmitting station 20d is inputted to the first repeating
station 30d, the transmission light is split into .lambda.1L and
.lambda.2PL by a demultiplexer 38a. The split .lambda.1L is
outputted as it is. A level of the split .lambda.2PL is adjusted by
the variable attenuator (attenuator) 38b. The .lambda.1L and
attenuated .lambda.2PL are multiplexed by an optical coupler 50
(not shown), inputted to the first optical amplifier 31a, and
optically amplified with residual pumping light (not shown) by the
first optical amplifier 31a. The optically amplified optical signal
(.lambda.1L'+.lambda.2PL') is branched toward a first loopback
filter 32b and an isolator 31c.
[0204] Light outputted from the isolator 31c is sent as it is to
the second repeating station 30d'. Only .lambda.2PL' of the other
light is extracted by the first loopback filter 32b, and this
component is sent back to the transmitting station 20d.
[0205] Inputted light (.lambda.1R'+.lambda.3PR'+.lambda.2PL") from
the second repeating station 30d' is inputted to a third filter 33d
and the sixth filter 64a. After a .lambda.2PL" component is removed
by the third filter 33d, the inputted light is split into
.lambda.1R' and .lambda.3PR' by a demultiplexer 39a. The split
.lambda.1R' is outputted as it is, whereas a level of the split
.lambda.3PR' is adjusted by the variable attenuator (attenuator)
39b, then they are multiplexed by an optical coupler 50 (not
shown), and inputted to a second optical amplifier 33c. The light
is optically amplified with residual pumping light (not shown) by
the second optical amplifier 33c. The amplified optical signal
(.lambda.1R"+.lambda.3PR") is branched toward an isolator 33a and a
second loopback filter 34a (filter 4).
[0206] The light outputted from the isolator 33a is sent as it is
to the transmitting station 20d. Only a .lambda.3PR" component of
the other light is extracted by the second loopback filter 34a, and
this component is sent back to the second repeating station
30d'.
[0207] Only the .lambda.2PL component of the inputted light from
the second repeating station 30d' is extracted by the sixth filter
(filter 6) 64a, and a reception level of this component is
monitored by the second optical detector (photodiode 2) 64b.
[0208] Next, a control in the second repeating station 30d' will be
described with reference to FIG. 11. FIG. 11 is a diagram showing
an internal structure of the second repeating station 30d'
according to the fourth modification of the first embodiment of
this invention. Like the second disconnect detecting means 64 in
the first repeating station 30d, the second repeating station 30d'
shown in FIG. 11 comprises a second disconnect detecting means 65,
and attenuation control units 70c and 70d.
[0209] The second disconnect detecting means 65 is disposed at the
entrance of the first optical fiber in order to detect a level of a
transmitted optical signal, thereby detecting cut of the second
optical fiber. The second disconnect detecting means 65 comprises a
fifth filter (filter 5) 65a extracting residual pumping light
(.lambda.3PR") from a transmitted optical signal and outputting it,
and a third optical detector (photodiode 3) 65a detecting a level
of the residual pumping light (.lambda.3PR") outputted from the
fifth filter 65a.
[0210] The attenuation control units 70c and 70d control the
variable attenuators (attenuators) 38b and 39b, respectively,
whereby an attenuation quantity of the second pumping light
adjusting means is controlled on the basis of a difference between
a level detected by the third optical detector 65b and a level
beforehand prepared.
[0211] At an entrance of the demultiplexer 38a disposed is a first
filter (filter 1) 31d. The first filter 31d removes a residual
pumping light component (.lambda.3PR") from the received optical
signal.
[0212] Accordingly, a first optical transmitting means 31 (refer to
FIG. 2) is provided with the first filter 31d which is disposed at
the input's side of the first optical amplifier 31a to remove the
residual pumping light component (.lambda.3PR") from a received
optical signal. The Others designated by like reference characters
have like or corresponding functions described above, further
descriptions of which are thus omitted.
[0213] In the second repeating station 30d' a control as follows is
performed. Transmission light (.lambda.1L'
+.lambda.2PL'+.lambda.3PL") from the first repeating station 30d is
inputted to the second repeating station 30d', and branched toward
the first filter 31d and the fifth filter 65a. The .lambda.1L'
component and the .lambda.2PL' component of the inputted light are
extracted by the first filter 31d, and split into .lambda.1L' and
.lambda.2PL' by the demultiplexer 38a.
[0214] The splits .lambda.1L' is outputted as it is. A level of the
other split .lambda.2PL' is adjusted by the variable attenuator
38b, multiplexed by an optical coupler 50 (not shown), inputted to
the first optical amplifier 31a, then optically amplified with
residual pumping light (not shown) by the first optical amplifier
31a. The optically amplified optical signal
(.lambda.1L"+.lambda.2PL") is branched toward the isolator 31c and
the first loopback filter 32b.
[0215] The light outputted from the isolator 31c is sent as it is
to the receiving station 40d. The .lambda.2PL" component of the
other light is extracted by the first loopback filter 32b, and this
component is send back to the first repeating station 30d.
[0216] Only the .lambda.3PR" component of the inputted light is
extracted by the fifth filter 65a, and the reception level is
monitored by the third optical detector 65b.
[0217] The opposite direction is similar. Namely, inputted light
(.lambda.1R+.lambda.3PR) from the receiving station 40d is split
into .lambda.1R and .lambda.3PR by the demultiplexer 39a. The split
.lambda.1R is inputted as it is to the second optical amplifier
33c. A level of the split .lambda.3PR is adjusted by the variable
attenuator (attenuator) 39b, multiplexed by an optical coupler 50
(not shown), then inputted to the second optical amplifier 33c.
[0218] .lambda.3PR is optically amplified with residual pumping
light (not shown) by the second optical amplifier 33c, and the
optically amplified optical signal (.lambda.1R'+.lambda.3PR') is
branched toward the isolator 33a and the second loopback filter
34a. The light outputted from the isolator 33a is sent as it is to
the first repeating station 30d. Only the .lambda.3PR' component of
the other light is extracted by the second loopback filter 34a, and
this component is sent back to the receiving station 40d.
[0219] With the above structure, repeater transmission is
performed. An operation of the first repeating station 30d (refer
to FIG. 10) is as follows.
[0220] First, an actual transmission loss value (value displayed on
the display unit 53a in the transmitting station 20d ) between the
transmitting station 20d and the first repeating station 30d, and
an optical output level value of .lambda.2PL' to be sent to the
second repeating station 30d' are sent to the attenuation control
unit (ATT1 control unit) 70a in the first repeating station 30d
from the transmitting station 20d. Incidentally, this actual
transmission loss value is expressed as photodiode 2 monitor value
in FIG. 10.
[0221] Next, the attenuation control unit 70a controls an optical
attenuation quantity at the variable attenuator 39b on the basis of
the actual transmission loss value between the transmitting station
20d and the first repeating station 30d so that .lambda.1R" at the
optimum level is inputted to the transmitting station 20d.
[0222] The attenuation control unit 70a' calculates an actual
transmission loss value between the first repeating station 30d and
the second repeating station 30d' on the basis of a difference
between an optical output level value of .lambda.2PL' to be sent to
the second repeating station 30d' and returned light .lambda.2PL"
(monitor value at the second optical detector 64b) from the second
repeating station 30d', and controls an optical attenuation
quantity at the variable attenuator 38b so that .lambda.1PL' at the
optimum level is inputted to the second repeating station 30d'.
[0223] Similarly, an operation of the second repeating station 30d'
(refer to FIG. 11) is as follows. First, an actual transmission
loss value (value displayed on the display unit 53b in the
receiving station 40d) between the receiving station 40 and the
second repeating station 30d', and an optical output level value of
.lambda.3PR' to be sent to the receiving station 40d are
transmitted to the attenuation control unit 70c.
[0224] The attenuation control unit 70c controls an optical
attenuation quantity at the variable attenuator 38b on the basis of
the actual transmission loss value between the receiving station
40d and the second repeating station 30d' so that .lambda.1L" at
the optimum level is inputted to the receiving station 40d.
[0225] The attenuation control unit 70d calculates an actual
transmission loss value between the second repeating station 30d'
and the first repeating station 30d on the basis of returned light
.lambda.3PR" (monitor value at the fifth filter 65a) from the first
repeating station 30d and an optical output level value of
.lambda.3PR', and controls an optical attenuation quantity at the
variable attenuator 39b so that .lambda.1R' at the optimum level is
inputted to the first repeating station 30d.
[0226] In the transmitting station 20d shown in FIG. 9, the
transmission light .lambda.1L is multiplexed with .lambda.2PL from
the first pumping source 22d, optically amplified by the optical
amplifier 22b, then transmitted along with residual pumping light
to the first repeating station 30d via an optical coupler 51.
[0227] The first repeating station 30d sends the amplified
transmission light .lambda.1L' and the amplified pumping light
.lambda.2PL' to the second repeating station 30d', and sends back
the amplified pumping light .lambda.2PL' to the transmitting
station 20d.
[0228] The second repeating station 30d' sends amplified
transmission light .lambda.1L" and amplified pumping light
.lambda.2PL" to the receiving station 40d, and sends back the
amplified pumping light .lambda.2PL" to the first repeating station
30d.
[0229] The opposite direction is similar. The second repeating
station 30d' amplifies transmission light (.lambda.1R+.lambda.3PR)
from the receiving station 40d, and outputs transmission light
(.lambda.1R'+.lambda.3PR') to the first repeating station 30d. The
second repeating station 30d' also sends back amplified pumping
light .lambda.3PR' to the receiving station 40d.
[0230] The first repeating station 30d amplifies the transmission
light (.lambda.1R'+.lambda.3PR'), and outputs transmission light
(.lambda.1R"+.lambda.3PR") to transmitting station 20d, and sends
back amplified pumping light .lambda.3PR" to the second repeating
station 30d'.
[0231] A gain controlling method in each of sections denoted by
{circle over (1)} through {circle over (5)} in FIG. 9 will be next
described. The controls in the sections {circle over (1)} through
{circle over (5)} are as follows:
[0232] {circle over (1)}: Optical output level control between the
transmitting station 20d and the first repeating station 30d;
optical output level control between the receiving station 40 and
the second repeating station 30d';
[0233] {circle over (2)}: Optical output level control between the
first repeating station 30d and the transmitting station 20d;
[0234] {circle over (3)}: Optical output level control between the
first repeating station 30d and the second repeating station
30d';
[0235] {circle over (4)}: Optical output level control between the
second repeating station 30d' and the receiving station 40;
[0236] {circle over (5)}: Optical output level control between the
second repeating station 30d' and the first repeating station
30d.
[0237] (i) With respect to {circle over (1)}
[0238] The controlling means 25 in the transmitting station 20d
calculates an optical output level of .lambda.2PL and stores it,
and is inputted thereto a level (value monitored by the second
optical detector 24b) of returned light .lambda.2PL' from the first
repeating station 30d. The controlling means 25 calculates an
actual transmission loss in {circle over (1)} from the above
result, and stores it. The displaying unit 53a displays this
result, while calculating an optical output level of .lambda.2PL'
at the first repeating station 30d using the relationship between
an optical level AIN inputted to the first optical amplifier 31a
and an optical amplification factor A, and displaying it.
[0239] The calculation is performed as shown by the above equations
(1) and (2). The control unit 25 in the transmitting station 20d
controls on the basis of an actual transmission loss obtained
through this calculation so that .lambda.1L at the optimum level is
inputted to the first repeating station 30d. Incidentally, an
operation of the control unit 45 in the receiving station 40d is
similar.
[0240] (ii) with respect to {circle over (2)}
[0241] The actual transmission loss value between the transmitting
station 20d and the first repeating station 30d and the optical
output level value of .lambda.2PL' displayed on the controlling
means 25 in the transmitting station 20d are inputted to both of
the attenuation control unit 70a and the attenuation control unit
70a' in the first repeating station 30d. The attenuation control
unit 70a controls on the basis of the inputted actual transmission
loss value between the transmitting station 20d and the first
repeating station 30d so that .lambda.1R" at the optimum level is
inputted to the transmitting station 20d.
[0242] (iii) with respect to {circle over (3)}
[0243] The attenuation control unit 70a in the first repeating
station 30d calculates an actual transmission loss value between
the first repeating station 30d and the second repeating station
30d' on the basis of the optical output level of the inputted
.lambda.2PL' and a monitor value at the second optical detector 64b
in the first repeating station 30d, and controls so that
.lambda.1L' at the optimum level is inputted to the second
repeating station 30d'.
[0244] (iv) with respect to {circle over (4)}
[0245] The actual transmission loss value between the receiving
station 40d and the second repeating station 30d' and the optical
output level value of .lambda.3PR' displayed on the controlling
means 45 in the receiving station 40d are inputted to both of the
attenuation control unit 70c and the attenuation control unit 70d
in the second repeating station 30d'. The attenuation control unit
70c controls on the basis of the inputted actual transmission value
between the receiving station 40d and the second repeating station
30d' so that .lambda.1L" at the optimum level is inputted to the
receiving station 40d.
[0246] (v) with respect to {circle over (5)}
[0247] The attenuation control unit 70d in the second repeating
station 30d' calculates an actual transmission loss value between
the second repeating station 30d' and the first repeating station
30d on the basis of an optical output level value of the inputted
.lambda.3PR' and a monitor value at the third optical detector 65b
in the second repeating station 30d', and controls so that
.lambda.1R' at the optimum level is inputted to the first repeating
station 30d.
[0248] As this, communication is performed among the stations using
only the optical cables in one system, and the output level of the
pumping source is automatically controlled in each of the stations,
which allows the optimum communication.
[0249] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect cut of the optical cable, so that reliability and safety of
this optical system 10d are remarkably improved.
[0250] (A5) Description of Fifth Modification of First Embodiment
of the Invention
[0251] In the optical system 10d according to the fourth
modification, an optical output level value after amplified by each
optical amplifier (EDFA) is determined on the basis of
characteristic data of the EDFA in a theoretical calculation.
According to this modification, not in the theoretical calculation
but using a monitoring function for outputted light, a more
accurate gain control becomes possible. This monitoring function is
performed by actual measurement using an optical detector
(photodiode).
[0252] FIG. 12 is a diagram showing a structure of an optical
system according to a fifth modification of the first embodiment of
this invention. An optical system 10e shown in FIG. 12 is a system
in which transmission light, a reception light and pumping light
can be transmitted/received through optical fiber cables in one
system. The optical system 10e comprises a transmitting station (A
station) 20e, a first repeating station (repeater 1) 30e, a second
repeating station (repeater 2) 30e' and a receiving station (B
station) 40e, where the stations are connected by optical cables,
whereby optical signals are transmitted/received in two ways.
[0253] When the optical system 10e shown in FIG. 12 is compared
with the optical system 10d shown in FIG. 9, the transmitting
station 20e is equivalent to the transmitting station 20d (refer to
FIG. 9) to which a level monitoring means 23 is additionally
provided. And, the displaying function is simplified. The receiving
station 40e is equivalent to the receiving station 40d (refer to
FIG. 9) to which a level monitoring means 43 is additionally
provided. And, the displaying function is simplified, as well. In
FIG. 12, parts designated by like reference characters have like or
corresponding functions, further descriptions of which are thus
omitted.
[0254] In FIG. 12, a wavelength of transmission light of the
transmitting station 20e is .lambda.1L, a wavelength of a first
pumping source 22d is .lambda.2PL, a wavelength of transmission
light of the receiving station 40e is .lambda.1R, and a wavelength
of a second pumping source 42d is .lambda.3PR.
[0255] Transmission light .lambda.1L from the transmitting station
20e is multiplexed with a first pumping source 22d, optically
amplified by an optical amplifier 22b, and transmitted along with
residual pumping light to the first repeating station 30e via an
optical coupler 51.
[0256] In the first repeating station 30e, the component of the
transmission light .lambda.1L of the light of the amplified
residual pumping light is removed by a first loopback filter 32b,
and an optical level thereof is monitored by a first optical
detector (photodiode 1) 32c, as will be described later.
[0257] The amplified transmission light .lambda.1L' and the
amplified pumping light .lambda.2PL' from the first repeating
station 30e are sent to the second repeating station 30e', and the
amplified pumping light .lambda.2PL' is sent back to the
transmitting station 20e. Like the fourth modification, an actual
transmission loss between the transmitting station 20e and the
first repeating station 20e is calculated, and an output level of
the pumping source 22d is controlled so as to yield the optimum
amplification factor.
[0258] In the second repeating station 30e', reception light
(.lambda.1L'+.lambda.2PL') from the transmitting station 20e is
amplified, amplified transmission light .lambda.1L" and amplified
pumping light .lambda.2PL" are sent to the receiving station 40e,
and the amplified pumping light .lambda.2PL" is sent back to the
first repeating station 30e. An actual transmission loss between
the first repeating station 30e and the second repeating station
30e' is calculated, a level of an optical attenuation quantity at
the first repeating station 30e is adjusted so as to yield the
optimum amplification factor, and an output level of the pumping
source (not shown) is controlled.
[0259] Flow of transmission light from the receiving station 40e is
similar.
[0260] FIG. 13 is a diagram showing an internal structure of the
first repeating station 30e according to the fifth modification of
the first embodiment of this invention. The first repeating station
30e shown in FIG. 13 has a similar structure to the first repeating
station 30e (refer to FIG. 10), which comprises a first loopback
means 32' and a second loopback means 34'. The function of a second
optical transmitting means in the first repeating station 30e is
realized by a third filter 33d disposed at an input's side of a
second optical amplifier 33c to remove a residual pumping light
component (.lambda.2PL") from a received optical signal, a second
pumping light adjusting means 39 and a second optical amplifier 33c
in cooperation. The first loopback means 32' is connected to a
first optical amplifier 31a to extract second pumping light
(.lambda.2PL') from an optical signal amplified by the first
optical amplifier 31a, outputs second pumping light (.lambda.2PL'),
and monitors a level of the same. The first loopback means 32'
comprises a first loopback filter 32b, an isolator 32a, and the
first optical detector (photodiode 1) 32c. The first loopback means
32' is similar to the above first loopback means 32 (refer to FIG.
2), in which an output from the first loopback filter 32b is
monitored.
[0261] The second loopback means 34' is similar to the above second
loopback means 34 (refer to FIG. 2), having a monitoring function.
The other parts designated by like reference characters have like
or corresponding functions, further descriptions of which are thus
omitted.
[0262] Accordingly, the first loopback means 32' has the first
optical detector 32c detecting a level of pumping light
(.lambda.2PL') outputted from the first optical amplifier 31a, and
controls an attenuation quantity of a first pumping light adjusting
means 38 on the basis of a level value detected by the first
optical detector 32c. The second loopback means 34' has a fourth
optical detector 34c detecting a level of pumping light
(.lambda.3PR") outputted from the second optical amplifier 33c to
control an attenuation quantity of the second pumping light
adjusting means 39 on the basis of a level value detected by the
fourth optical detector 34c.
[0263] In the first repeating station 30e, the following control is
performed. When transmission light (.lambda.1L+.lambda.2PL) from
the transmitting station 20e is inputted to the first repeating
station 30e, the transmission light is split into .lambda.1L and
.lambda.2PL by a demultiplexer 38e. The split .lambda.1L is
outputted as it is. A level of the split .lambda.2PL is adjusted by
a variable attenuator 38b, outputted, multiplexed with .lambda.1L
by an optical coupler 50 (not shown), and inputted to the first
optical amplifier 31a. The light signal (.lambda.1L'+.lambda.2PL")
optically amplified with residual pumping light (not shown) by the
first optical amplifier 31a is branched toward the isolator 31c and
the first loopback filter 32b. The light toward the isolator 31c is
sent as it is to the second repeating station 30e', whereas a
.lambda.2PL' component of the light toward the first loopback
filter 32b is extracted by the first loopback filter 32b, and sent
back to the transmitting station 20e. At this time, an optical
level of the amplified residual pumping light (.lambda.2PL') is
monitored by the first optical detector 32c.
[0264] Inputted light (.lambda.1R'+.lambda.3PR'+.lambda.2PL") from
the second repeating station 30e is inputted to the third filter
33d and a sixth filter 64a, and a .lambda.2PR" component is removed
by the third filter 33d. The light is then split into .lambda.1R'
and .lambda.3PR' by a demultiplexer 39a. The split .lambda.1R' is
outputted as it is, whereas a level of the split .lambda.3PR' is
adjusted by a variable attenuator 39b, multiplexed with .lambda.1R'
by an optical coupler 50 (not shown), then inputted to the second
optical amplifier 33c.
[0265] The light is optically amplified with residual pumping light
(not shown) by the second optical amplifier 33c. The optically
amplified optical signal (.lambda.1R"+.lambda.3PR") is branched
toward the isolator 33a and a second loopback filter 34a. The light
toward the isolator 33a is sent as it is to the transmitting
station 20e, whereas only a .lambda.3PR" component of the light
toward the second loopback filter 34a is extracted by the second
loopback filter 34a. This component is sent back to the second
repeating station 30e'. At this time, an optical level of the
amplified residual pumping light .lambda.3PR" is monitored by a
fourth optical detector 44b.
[0266] On the other hand, only a .lambda.2PL component of the
inputted light from the second repeating station 30e' to be
inputted to the sixth filter 64a is extracted by the sixth filter
64a. A reception level of this component is monitored by the second
optical detector.
[0267] FIG. 14 is a diagram showing an internal structure of the
second repeating station 30e' according to the fifth modification
of the first embodiment of this invention. The second repeating
station 30e' shown in FIG. 14 has a similar structure to the second
repeating station 30d' (refer to FIG. 11), which comprises a first
loopback means 32', and the second loopback means 34', having a
monitoring function. In FIG. 14, parts designated by like reference
characters have like or corresponding functions described above,
further descriptions of which are thus omitted.
[0268] In the second repeating station 30e', the following control
is performed. When transmission light
(.lambda.1L'+.lambda.2PL'+.lambda.3PR"- ) from the first repeating
station 30e is inputted to the second repeating station 30e', the
transmission light is branched toward a first filter 31d and a
fifth filter 65a at an entrance leading to the first repeating
station 30e. In the inputted light toward the first filter 31d,
.lambda.1L' component and a .lambda.2PL' component are extracted by
the first filter 31d, and split into .lambda.1L' and .lambda.2PL'
by the demultiplexer 38a. The split .lambda.1L' is outputted as it
is. A level of the split .lambda.2PL' is adjusted by a variable
attenuator 38b. After that, .lambda.2PL' is multiplexed with
.lambda.1L' by an optical coupler 50 (not shown), inputted to a
first optical amplifier 31a, and optically amplified with residual
pumping light (not shown) by the first optical amplifier 31a. The
optically amplified optical signal (.lambda.1L"+.lambda.2PL") is
branched toward an isolator 31c and the first loopback filter 32b.
The light toward the isolator 31c is sent as it is to the receiving
station 40e. Only a .lambda.2PL" component of the other light is
extracted by the first loopback filter 32b. This component is sent
back to the first repeating station 30e. At this time, an optical
level of the amplified residual pumping light .lambda.2PL" is
monitored by the first optical detector 32c.
[0269] Only a .lambda.3PR component of the other light inputted
toward the fifth filter 65a is extracted by the fifth filter 65a,
and a reception level of the same is monitored by a third optical
detector 65b.
[0270] The opposite direction is similar. Namely inputted light
(.lambda.1R+.lambda.3PR) from the receiving station 40e is split
into .lambda.1R and .lambda.3PR by a demultiplexer 39a. The split
.lambda.1R is outputted as it is. A level of the other split
.lambda.3PR is adjusted by a variable attenuator 39b, .lambda.3PR
is multiplexed with .lambda.1R by an optical coupler 50 (not
shown), inputted to a second optical amplifier 33c, optically
amplified with residual pumping light (not shown) by the second
optical amplifier 33c. The optically amplified optical signal
(.lambda.1R'+.lambda.3PR') is branched toward an isolator 3 and a
second loopback filter 34a. The light toward the isolator 3 is sent
as it is to the first repeating station 30e. Only the .lambda.3PR'
component of the light toward the second loopback filter 34a is
extracted by the second loopback filter 34a. This component is sent
back to the receiving station 40e.
[0271] With the above structure, repeater transmission is
performed. In FIG. 12, an operation of a controlling means 25 in
the transmitting station 20e is as follows. An optical output level
of .lambda.2PL is monitored by a first optical detector 23b. A
level of returned light .lambda.2PL' from the first repeating
station 30e is monitored by a second optical detector 24b. In the
method described in the fourth embodiment, an actual transmission
loss between the transmitting station 20e and the first repeating
station 30e is calculated, and displayed on a display unit 53a. The
controlling means 25 performs a gain control on the first pumping
source 22d so that the optimum optical level is inputted to the
first repeating station 30e.
[0272] An operation of the controlling means 45 in the receiving
station 40e is as follows. An optical output level of .lambda.3PR
is monitored by a third optical detector (photodiode 3) 43b.
Returned light .lambda.3PR' from the second repeating station 30e '
is monitored by a fourth optical detector (photodiode 4) 44b. In
the method described in the fourth embodiment, an actual
transmission loss value between the receiving station 40e and the
second repeating station 30e' is calculated, and displayed on a
displaying unit 53b. The controlling means 45 performs a gain
control on a second pumping source 42b so that the optimum optical
level is inputted to the second repeating station 30e'.
[0273] Operations of attenuation control units 70a and 70a' in the
first repeating station 30e are as follows. In FIG. 13, an actual
transmission loss value (displayed on the controlling means 25 in
the transmitting station 20e ) between the transmitting station 20e
and the first repeating station 30e is inputted to the attenuation
control unit 70a' which adjusts an output optical level toward the
transmitting station 20e. The attenuation control unit 70a'
controls an optical attenuation quantity of the variable attenuator
39b on the basis of the inputted actual transmission loss value
between the transmitting station 20e and the first repeating
station 30e so that .lambda.1R" at the optimum level is inputted to
the transmitting station 20e.
[0274] The attenuation control unit 70a (adjusting an output
optical level toward the first repeating station 30e ) calculates
an actual transmission loss value between the first repeating
station 30e and the second repeating station 30e' on the basis of a
difference between a monitor value (an optical output level value
of .lambda.2PL' to the second repeating station 30e') of the first
optical detector 32c and a monitor value (returned light
.lambda.2PL" from the second repeating station 30e') of the second
optical detector 64a, and controls an optical attenuation quantity
of the variable attenuator 38b so that .lambda.1L ' at the optimum
level is inputted to the second repeating station 30e'.
[0275] Similarly, operations of attenuation control units 70c and
70d in the second repeating station 30e ' are as follows. In FIG.
14, an actual transmission loss value between the receiving station
40e and the second repeating station 30e' displayed on a
controlling means 45 in the receiving station 40e is inputted to
the attenuation control unit 70d. The attenuation control unit 70
controls an optical attenuation quantity of the variable attenuator
38b on the basis of the inputted actual transmission loss value
between the receiving station 40e and the second repeating station
30e ' so that .lambda.1L" at the optimum level is inputted to the
receiving station 40e.
[0276] The attenuation control unit 70c (adjusting an output
optical level to the first repeating station 30e) calculates an
actual transmission loss value between the second repeating station
30e' and the first repeating station 30e on the basis of a
difference between a monitor value (optical output value of
.lambda.3PR' to the first repeating station 30e) of the fourth
optical detector 44b and a monitor value of the third optical
detector 65b (returned light .lambda.3PR" from the first repeating
station 30e), and controls an attenuation quantity of the variable
attenuator 39b so that .lambda.1R' at the optimum level is inputted
to the first repeating station 30e.
[0277] Sections denoted by {circle over (1)} through {circle over
(5)} shown in FIG. 12 are defined as follows, and gain controls in
the respective sections will be now described.
[0278] {circle over (1)}: Optical output level control between the
transmitting station 20e and the first repeating station 30e,
optical level control between the receiving station 40e and the
second repeating station 30e';
[0279] {circle over (2)}: Optical output level control between the
first repeating station 30e and the transmitting station 20e;
[0280] {circle over (3)}: Optical output level control between the
first repeating station 30e and the second repeating station
30e';
[0281] {circle over (4)}: Optical output level control between the
second repeating station 30e' and the receiving station 40e;
[0282] {circle over (5)}: Optical output level control between the
second repeating station 30e' and the first repeating station
30e.
[0283] (i) with respect to {circle over (1)}
[0284] The controlling means 25 in the transmitting station 20e
monitors an optical output level of .lambda.2PL by the first
optical detector 23b and stores it, and monitors a level of
returned light .lambda.2PL' from the first repeating station 30e by
the second optical detector 24b. The controlling means 25
calculates an actual transmission loss in {circle over (1)} on the
basis of the above result and displays it, and controls on the
basis of the actual transmission loss value obtained in the above
calculation so that .lambda.1L and .lambda.2PL at the optimum
levels are inputted to the first repeating station 30e.
Incidentally, an operation of a controlling means 45 in the
receiving station 40e is similar.
[0285] (ii) with respect to {circle over (2)}
[0286] An actual transmission loss value (displayed on the
controlling means 25 in the transmitting station 20e) between the
transmitting station 20e and the first repeating station 30e is
inputted to an attenuation control unit 70a in the first repeating
station 30e. The attenuation control unit 70a controls on the basis
of the inputted actual transmission loss value between the
transmitting station 20e and the first repeating station 30e so
that .lambda.1R" at the optimum level is inputted to the
transmitting station 20e.
[0287] (iii) with respect to {circle over (3)}
[0288] The variable attenuator 38b control unit in the first
repeating station 30e calculates an actual transmission loss value
between the first repeating station 30e and the second repeating
station 30e' on the basis of an optical output level value
monitored by the first optical detector in the first repeating
station 30e and a monitor value of the second optical detector in
the first repeating station 30e, and controls so that .lambda.1L'
at the optimum level is inputted to the second repeating station
30e'.
[0289] (iv) with respect to {circle over (4)}
[0290] An actual transmission loss value (displayed on the control
unit 45 in the receiving station 40e ) between the receiving
station 40e and the second repeating station 30e' is inputted to
the attenuation control unit 70c in the second repeating station
30e'. The attenuation control unit 70c controls on the basis of the
inputted actual transmission loss value between the receiving
station 40e and the second repeating station 30e' so that
.lambda.1L" at the optimum level is inputted to the receiving
station 40e.
[0291] (v) with respect to {circle over (5)}
[0292] The attenuation control unit 70a in the second repeating
station 30e' calculates an actual transmission loss value between
the second repeating station 30e' and the first repeating station
30e on the basis of an output level value monitored by the fourth
optical detector 44b in the second repeating station 30e' and a
monitor value of the third optical detector 65b in the second
repeating station 30e', and controls so that .lambda.1R' at the
optimum value is inputted to the first repeating station 30e.
[0293] As this, communication is performed among the stations using
only optical cables in one system, and the output level of the
pumping source is automatically controlled in each of the stations,
which allows the optimum communication.
[0294] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect cut of the optical cable so that reliability and safety of
this optical system 10e is remarkably improved.
[0295] (A6) Description of Sixth Modification of First Embodiment
of the Invention
[0296] FIG. 15 is a diagram showing a structure of an optical
system according to a sixth modification of the first embodiment of
this invention. An optical system 10f shown in FIG. 15 has
different values of wavelengths for use in transmission, as
compared with the above optical system 10d. Namely, different
points are that the wavelength .lambda.2PL' and the wavelength
.lambda.2PL" used in the above optical system 10d are replaced with
a wavelength .lambda.2PL, and the wavelength .lambda.3PR' and the
wavelength .lambda.3PR" are replaced with a wavelength .lambda.3PR.
In FIG. 15, parts designated by like reference characters have like
or corresponding functions described above, further descriptions of
which are thus omitted.
[0297] FIG. 16 is a diagram showing an internal structure of a
first repeating station 30f according to the sixth modification of
the first embodiment of this invention. The first repeating station
30f shown in FIG. 16 monitors a value of a received optical
wavelength in lieu of a variable attenuator, thereby adjusting
output optical levels of a first optical amplifier 31a and a second
optical amplifier 33c.
[0298] The first repeating station 30f is provided with a first
pumping light generating means 66 disposed on the input's side of a
first optical amplifier 31a (in an upper part in FIG. 16). The
first pumping light generating means 66 comprises a first pumping
source (pumping source 1) 66a and a first pumping light controlling
means (control unit) 66b. The first repeating station 30f is also
provided with a second pumping light generating means 64' on a
input's side of the second optical amplifier 33c (in a lower part
in FIG. 16). The second pumping light generating means 64'
comprises a second pumping source (pumping source 2) 64'a, a second
pumping light controlling means (control unit) 64'b, and a
displaying unit 64'c.
[0299] The first pumping light controlling means 66b controls an
output level of the first pumping source 66a. The second pumping
light controlling means 64'b controls an output level of the second
pumping source 64'a. The displaying unit 64'c is connected to the
second pumping light controlling means 64'b to display an optical
output level value of .lambda.3PR, a display apparatus (not shown),
for example, being used therefor.
[0300] The first optical amplifier 31a, an isolator 31c and the
first pumping light generating means 66 function in cooperation as
a first optical transmitting means. The second optical amplifier
33c, an isolator 33a and the second pumping light generating means
64' function in cooperation as a second optical transmitting
means.
[0301] Accordingly, the second optical transmitting means (33c,
33a, 64') is provided with a second displaying means (display unit
64'c) which has control data relating to a second transmission loss
value that an optical signal loses on the transmission path, and
can output the control data, and a second pumping light controlling
means 64'b which controls an output level of the second pumping
source 64'a in its station on the basis of the control data of the
second displaying means (display unit 64'c). In FIG. 16, parts
designated by like reference characters have like or corresponding
described above, further descriptions of which are thus
omitted.
[0302] FIG. 17 is a diagram showing an internal structure of a
second repeating station 30f' according to the sixth modification
of the first embodiment of this invention. The second repeating
station 30f' shown in FIG. 17 monitors a value of a received
optical wavelength in lieu of a variable attenuator, thereby
adjusting output optical levels of the first optical amplifier 31a
and the second optical amplifier 33c.
[0303] In the second repeating station 30f', a first pumping light
generating means 66' is disposed on the input's side of a first
optical amplifier 31a (in the upper part in FIG. 17). The first
pumping light generating means 66' comprises a first pumping source
(pumping source 1) 66a, a first pumping light controlling means
(control unit) 66b and a displaying unit (.lambda.2PL optical
output level value display) 66c. In the second repeating station
30f', a second pumping light generating means 64 is disposed on the
input's side of a second optical amplifier 33c (in the lower part
in FIG. 17). The second pumping light generating means 64 comprises
a second pumping source (pumping source 2) 64a and a second pumping
light controlling means (control unit) 64b.
[0304] The displaying unit 66c is connected to the first pumping
light controlling means 66b to display an optical output level of
.lambda.2PL, a display apparatus (not shown) being used therefor.
The first optical amplifier 31a, the isolator 31c and the first
pumping light generating means 66' function in cooperation as a
first optical transmitting means. The second optical amplifier 33c,
an isolator 33a and the second pumping light generating means 64
function in cooperation as a second optical transmitting means. In
FIG. 17, parts designated by like reference characters have like or
corresponding functions described above, further descriptions of
which are thus omitted.
[0305] Accordingly, the first optical transmitting means (31a, 31c,
66') is provided with a first displaying means (display unit 66c)
which has control data relating to a first transmission loss value
that an optical signal loses on the transmission path, and can
output the control data, and the first pumping light controlling
means 66b which controls an output level of the first pumping
source 66a in its own station on the basis of the control data of
the first displaying means (display unit 66c).
[0306] In FIG. 16, an optical signal transmitted from the
transmitting station 20f is inputted from the left side in FIG. 16.
Only a .lambda.1L component of this optical signal is extracted by
a first filter 31d, and outputted as it is. A level of a
.lambda.2PL component outputted from the first pumping source 66a
is adjusted by the first pumping light controlling means 66b,
outputted, multiplexed with the above .lambda.1L by an optical
coupler 50 (not shown), and inputted to the first optical amplifier
31a.
[0307] The optical signal (.lambda.1L'+.lambda.2PL) optically
amplified by the first optical amplifier 31a is branched toward the
isolator 31c and the first loopback filter 32b. The light toward
the isolator 31c is sent as it is to the second repeating station
30f'. Only the .lambda.2PL component of the light toward the first
loopback filter 32b is extracted by the first loopback filter 32b,
and this component is sent back to the transmitting station
20f.
[0308] Inputted light (.lambda.1R'+.lambda.3PR'+.lambda.2PL") from
the second repeating station 30f' is inputted to a third filter 33d
and the sixth filter 64a. A.lambda.1R" component of the inputted
light is removed by the third filter 33d, the inputted light is
then outputted as it is. A level of .lambda.3PR' is adjusted by the
second pumping light controlling means 64'b, multiplexed with the
above .lambda.1R', and inputted to the second optical amplifier
33c.
[0309] The optical signal (.lambda.1R"+.lambda.3PR) optically
amplified by the second optical amplifier 33c is branched toward
the isolator 33a and a second loopback filter 34a. The light toward
the isolator 33a is sent as it is to the transmitting station 20f.
Only a .lambda.3PR component of the other light is extracted by the
second loopback filter 34a. This component is sent back to the
second repeating station 30f'.
[0310] Only a .lambda.2PL component of inputted light from the
second repeating station 30f' to be inputted to the sixth filter
64a is extracted by the sixth filter 64a. A reception level of this
component is monitored by the second optical detector 64b.
[0311] Similarly, in FIG. 17, transmission light
(.lambda.1L'+.lambda.2PL +.lambda.3PR) from the first repeating
station 30f is inputted from the left side in the FIG. 17. When the
optical signal is inputted to the second repeating station 30f',
the optical signal is branched toward a first filter 31d and a
fifth filter 65a. Only a .lambda.1L' component of the light
inputted to the first filter 31d is extracted by the first filter
31d, and outputted as it is. A level of .lambda.2PL outputted from
a first pumping source 66a is adjusted by a first pumping light
controlling means 66b, outputted, multiplexed with the above
.lambda.1L' by an optical coupler 50 (not shown), and inputted to a
first optical amplifier 31a.
[0312] The optical signal (.lambda.1L"+.lambda.2PL) optically
amplified by the first optical amplifier 31a is branched toward the
isolator 31c and a first loopback filter 32b. The light toward the
isolator 31c is sent as it is to the receiving station 40f. Only a
.lambda.2PL component of the light toward the first loopback filter
32b is extracted by the first loopback filter 32b, and this
component is sent back to the repeating station 30f.
[0313] Only a .lambda.3PR component of the inputted light toward a
fifth filter 65a is extracted by the fifth filter 65a, and a
reception level thereof is monitored by a third optical detector
65b.
[0314] Only a .lambda.1R component of inputted light
(.lambda.1R+.lambda.3PR) from the receiving station 40f is
extracted by a third filter 33d, and inputted to a second optical
amplifier 33c. A level of .lambda.3PR is adjusted by a second
pumping light controlling means 64b. .lambda.3PR is multiplexed
with .lambda.1R by an optical coupler 50 (not shown), and inputted
to the second optical amplifier 33c. The optical signal
(.lambda.1R'+.lambda.3PR) optically amplified by the second optical
amplifier 33c is branched toward an isolator 33a and a second
loopback filter 34a. The light toward the isolator 33a is sent as
it is to the first repeating station 30f. Only a .lambda.3PR
component of the other light is extracted by the second loopback
filter 34a. This component is sent back to the receiving station
40f.
[0315] With the above structure, repeater transmission is
performed. In the first repeating station 30f shown in FIG. 16, a
value (actual transmission loss value between the transmitting
station 20f and the first repeating station 30f) displayed by a
controlling means 25 in the transmitting station 20f is inputted,
and this information is transmitted to the second pumping light
controlling means 64'b. The second pumping light controlling means
64'b performs a gain control on the second pumping source 64'a on
the basis of the inputted actual transmission loss value between
the transmitting station 20f and the first repeating station 30f so
that .lambda.1R" at the optimum level is inputted to the
transmitting station 20f.
[0316] The first pumping light controlling means 66b calculates an
actual transmission loss value between the first repeating station
30f and the second repeating station 30f' from a monitor value of
the second optical detector 64b and an optical output level value
of .lambda.2PL to be outputted to the second repeating station
30f', and performs a gain control on the first pumping source 64'a
so that .lambda.1L' at the optimum level is inputted to the second
repeating station 30f'.
[0317] Similarly, in the second repeating station 30f' shown in
FIG. 17, a value (actual transmission loss value between the
receiving station 40f and the second repeating station 30f')
displayed by a controlling means 45 in the receiving station 40f is
inputted, and this information is transmitted to the second pumping
light controlling means 64b. The first pumping light controlling
means 64b performs a gain control on the first pumping source 66a
on the basis of the inputted actual transmission loss value between
the receiving station 40f and the second repeating station 30f' so
that .lambda.1L" at the optimum level is inputted to the receiving
station 40f.
[0318] The second pumping light controlling means 64b calculates an
actual transmission loss value between the second repeating station
30f' and the first repeating station 30f on the basis of a monitor
value of the second optical detector 65b and an inputted optical
output level value of .lambda.3PR in the first repeating station
30f, and performs a gain control on the second pumping source 64a
so that .lambda.1R' at the optimum level is inputted to the first
repeating station 30f.
[0319] The gain controls in respective sections denoted by {circle
over (1)} through {circle over (5)}0 in FIG. 15 are as follows.
[0320] {circle over (1)}: Optical output level control between the
transmitting station 20f and the first repeating station 30,
optical output level control between the receiving station 40f and
the second repeating station 30f';
[0321] {circle over (2)}: Optical output level control between the
first repeating station 30f and the transmitting station 20f;
[0322] {circle over (3)}: Optical output level control between the
first repeating station 30f and the second repeating station
30f';
[0323] {circle over (4)}: Optical output level control between the
second repeating station 30f' and the receiving station 40f;
[0324] {circle over (5)}: Optical output level control between the
second repeating station 30f' and the first repeating station
30f.
[0325] (i) with respect to {circle over (1)}
[0326] The controlling means 25 in the transmitting station 20f
calculates an optical output level of .lambda.2PL, and stores it.
The optical output level value of .lambda.2PL displayed in the
first repeating station 30f is inputted to the controlling means 25
in the transmitting station 20f, and an actual transmission loss
between the transmitting station 20f and the first repeating
station 30f is calculated on the basis of a difference between the
optical output level value of .lambda.2PL and a monitor value of
the second optical detector 24b in the first repeating station 30f,
and displayed. The controlling means 25 in the transmitting station
20f controls on the basis of the actual transmission loss value
obtained in the above calculation so that .lambda.1L at the optimum
level is inputted to the first repeating station 30f.
[0327] Meanwhile, an operation of the controlling means 45 in the
receiving station 40f is similar.
[0328] (ii) with respect to {circle over (2)}
[0329] A value (actual transmission loss value between the
transmitting station 20f and the first repeating station 30f)
displayed on the controlling means 25 in the transmitting station
20f is inputted to the second pumping light controlling means 64'b
in the first repeating station 30f. The second pumping light
controlling means 64'b controls on the basis of the inputted actual
transmission loss value between the transmitting station 20f and
the first repeating station 30f so that .lambda.1R" at the optimum
level is inputted to the transmitting station 20f.
[0330] (iii) with respect to {circle over (3)}
[0331] the first pumping light controlling means 66b in the first
repeating station 30f calculates an actual transmission loss value
between the first repeating station 30f and the second repeating
station 30f' from an inputted optical output level value of
.lambda.2PL in the second repeating station 30f' and a monitor
value of the second optical detector 64b in the first repeating
station 30f, and controls so that .lambda.1L' at the optimum level
is inputted to the second repeating station 30f'.
[0332] (iv) with respect to {circle over (4)}
[0333] A value (actual transmission loss value between the
receiving station 40 and the second repeating station 30f')
displayed on the controlling means 45 in the receiving station 40f
is inputted to the first pumping light controlling means 66b in the
second repeating station 30f'. The first pumping light controlling
means 66b controls on the basis of the inputted actual transmission
loss value between the receiving station 40f and the second
repeating station 30f' so that .lambda.1L" at the optimum level is
inputted to the receiving station 40f.
[0334] (v) with respect to {circle over (5)}
[0335] The second pumping light controlling means 64'b in the
second repeating station 30f' calculates an actual transmission
loss value between the second repeating station 30f' and the first
repeating station 30f from an inputted optical output level value
of .lambda.3PR of the first repeating station 30f and a monitor
value of the third optical detector 65b in the second repeating
station 30f', and controls so that .lambda.1R' at the optimum level
is inputted to the first repeating station 30f.
[0336] As this, communication among the stations is performed using
only optical cables in one system, and the output level of the
pumping source is automatically controlled in each of the stations,
which allows the optimum communication.
[0337] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and reliability and safety of
this optical system 10f is remarkably improved since each of the
stations can detect cut of the optical cable.
[0338] (A7) Description of Seventh Modification of First Embodiment
of the Invention
[0339] Next, description will be made of another control mode of
the above optical system 10f (refer to FIG. 15).
[0340] FIG. 18 is a diagram showing an internal structure of a
first repeating station 30g according to a seventh modification of
the first embodiment of this invention. A difference between the
first repeating station 30g shown in FIG. 18 and the first
repeating station 30f shown in FIG. 16 is that the first repeating
station 30f computes an optical output level after amplified of the
pumping source from the database and displays it, whereas this
modification displays a result of measurement monitored by a
detector (photodiode) to enable a more accurate gain control.
[0341] A first loopback means 32" is connected to an output's side
of a first optical amplifier 31a (in the upper part in FIG. 18).
The first loopback means 32" is connected to the first optical
amplifier 31a to extract second pumping light (.lambda.2PL) from an
optical signal amplified by the first optical amplifier 31a, and
output second pumping light (.lambda.2PL). The first loopback means
32" comprises a first loopback filter 32b, an isolator 32a and a
first optical detector 32c, along with a display unit 32d. The
display unit 32d displays an optical output level value of
.lambda.2PL, a display apparatus, for example, being used
therefor.
[0342] A first pumping light controlling means 66b is provided with
the first level monitoring means 32c which detects a level of the
second pumping light (.lambda.2PL) outputted from the second filter
32b to control an output optical level of the first pumping source
31a on the basis of a level detected by the first level monitoring
means 32c and a reception light level detected by the first
reception light monitoring means. A second pumping light
controlling means 64'b is provided with a second level monitoring
means 34c which detects a level of third pumping light
(.lambda.3PR) outputted from a fourth filter 34a to control an
output optical level of a second pumping source 64'a on the basis
of a level value detected by the second level monitoring means 34c
and a reception light level detected by the first reception light
monitoring means.
[0343] In FIG. 18, parts designated by like reference characters
have like or corresponding functions described above, further
descriptions of which are thus omitted.
[0344] When transmission light (.lambda.1L+.lambda.2PL) from a
transmitting station 20f is inputted to the first repeating station
30g, only a .lambda.1L component thereof is extracted by a first
filter 31d, multiplexed with pumping light (.lambda.2PL) of the
first pumping source 22d, and inputted to the first optical
amplifier 31a. The optical signal (.lambda.1L'+.lambda.2PL)
optically amplified by the first optical amplifier 31a is
demultiplexed toward the isolator 31c and the first loopback filter
32b. The light toward the isolator 31c is sent as it is to the
second repeating station 30g'. Only a .lambda.2PL component of the
light toward the first loopback filter 32b is sent back to the
transmitting station 20f by the first loopback filter 32b. At this
time, an optical level of the amplified pumping light (.lambda.2PL)
is monitored by the first optical detector 32c and displayed.
[0345] Similarly, a second loopback means 34" is connected to an
output's side of the second optical amplifier 33c (in the lower
part in FIG. 18). The second loopback means 34" is connected to the
second optical amplifier 33c to extract .lambda.3PR from the
optical signal amplified by the second optical amplifier 33c, and
output .lambda.3PR. The second loopback means 34" comprises the
second loopback filter 34a, the isolator 32a and the first optical
detector 32c, along with the display unit 32d. The display unit 32d
displays an optical output level value of .lambda.2PL, a display
apparatus, for example, being used therefor.
[0346] Inputted light (.lambda.1R'+.lambda.3PR+.lambda.2PL) from
the second repeating station 30g' is inputted to a third filter 33d
and a sixth filter 64a. Only a .lambda.1R' component of this
inputted light is extracted by the third filter 33d, and outputted
as it is. A level of .lambda.3PR is adjusted by the second pumping
light controlling means 64'b, and .lambda.3PR is multiplexed with
the above .lambda.1R' by an optical coupler 50 (not shown), and
inputted to a second optical amplifier 33c. The optical signal
(.lambda.1R"+.lambda.3PR) optically amplified by the second optical
amplifier 33c is branched toward the isolator 33a and the second
loopback filter 34a. The light from the isolator 33a is sent as it
is to the transmitting station 20f. Only a .lambda.3PR component of
the light from the side of the second loopback filter 34a is
extracted from the second loopback filter 34a at the second
loopback filter 34a. Only a .lambda.2PL component of inputted light
from the second repeating station 30g' to be inputted to the sixth
filter 64a is extracted by the sixth filter 64a. A reception level
of this component is monitored by the second optical detector
64b.
[0347] FIG. 19 is a diagram showing an internal structure of the
second repeating station 30g' according to the seventh modification
of the first embodiment of this invention. A process inside the
second repeating station 30g' shown in FIG. 19 is as follows.
Namely, transmission light (.lambda.1L'+.lambda.2PL+.lambda.3PR)
from the first repeating station 30g is inputted to the second
repeating station 30g'. Only a .lambda.1L' component of this
inputted light is extracted by a first filter 31d, multiplexed with
pumping light (.lambda.2PL) of a first pumping source 22d via an
optical coupler 50, and inputted to a first optical amplifier 31a.
The optical signal (.lambda.1L"+.lambda.2PL) optically amplified by
the first optical amplifier 31a is demultiplexed toward an isolator
31c and an isolator 32a. The light toward the isolator 31c is sent
as it is to the receiving station 40f. Only a .lambda.2PL component
of the light toward a first loopback filter 32b is extracted by the
first loopback filter 32b. This component is sent back to the first
repeating station 30g.
[0348] At this time, an optical level of the amplified residual
pumping light .lambda.2PL is monitored by a first optical detector
32c and displayed. Only a .lambda.3PR component of the inputted
light toward a fifth filter 65a is extracted by the fifth filter
65a, and a reception level thereof is monitored by a third optical
detector 65b.
[0349] Only a .lambda.1R component of inputted light from the
receiving station 40f is extracted by a third filter 33d. This
.lambda.1R component is inputted to a second optical amplifier 33c.
A level of .lambda.3PR is adjusted by a second pumping light
controlling means 64b, multiplexed with .lambda.1R by an optical
coupler 50 (not shown), then inputted to a second optical amplifier
33c. The optical signal (.lambda.1R'+.lambda.3PR- ) optically
amplified by the second optical amplifier 33c is branched toward
the isolator 33a and a second loopback filter 34a. The light from
the isolator 33a is sent as it is to the first repeating station
30g. Only a .lambda.3PR component of the light toward the second
loopback filter 34a is extracted by the second loopback filter 34a,
and this component is sent back to the receiving station 40.
[0350] In FIG. 19, parts designated by like reference characters
have like or corresponding functions described above, further
descriptions of which are thus omitted.
[0351] With the above structure, a value (actual transmission loss
value between the transmitting station 20f and the first repeating
station 30g) displayed on the display unit 53a in the transmitting
station 20f is inputted to the first repeating station 30g (refer
to FIG. 18), and this information is transmitted to the second
pumping light controlling means 64'b. The second pumping light
controlling means 64'b performs a gain control on the second
pumping source 64'a on the basis of the inputted actual
transmission loss value between the transmitting station 20f and
the first repeating station 30g so that .lambda.1R" at the optimum
level is inputted to the transmitting station 20f.
[0352] The first pumping light controlling means 66b calculates an
actual transmission loss value between the first repeating station
30g and the second repeating station 30g' on the basis of a monitor
value of the second optical detector 64'b and the inputted optical
output level value of .lambda.2PL in the second repeating station
30g', and performs a gain control on the first pumping source 22d
so that .lambda.1L ' at the optimum level is inputted to the second
repeating station 30g'.
[0353] A value (actual transmission loss value between the
receiving station 40f and the second repeating station 30g')
displayed on the controlling means 45 in the receiving station 40f
is inputted to the second repeating station 30g' shown in FIG. 19,
and this information is transmitted to a first pumping light
controlling means 66b. The first pumping light controlling means
66b controls an optical attenuation quantity of the first pumping
source 66a on the basis of the inputted actual transmission loss
value between the receiving station 40f and the second repeating
station 30g' so that .lambda.1L" at the optimum level is inputted
to the receiving station 40f.
[0354] The second pumping light controlling means 64'b calculates
an actual transmission loss value between the second repeating
station 30g' and the first repeating station 30g from a monitor
value of the third optical detector 65b and an inputted optical
output level value of returned light .lambda.3PR from the first
repeating station 30g, and performs a gain control on the second
pumping source 64a so that .lambda.1R' at the optimum level is
inputted to the first repeating station 30g. A gain controlling
method in each of the sections is similar to that described in the
sixth modification of the first embodiment, further description of
which is thus omitted.
[0355] Accordingly, the output level of the pumping source in each
of the stations is controlled using only the optical cables in one
system, and each of the stations can detect cut of the optical
cable, which allows a large decrease in the installation cost and
maintenance cost of the optical cables.
[0356] (A8) Description of Eighth Modification of First
[0357] Embodiment of the Invention
[0358] It is possible to decrease the number of the used
wavelengths by providing a repeating station according to this
modification in the optical system 10c described in the first
modification of the first embodiment described above. In concrete,
the wavelength .lambda.2PL' and the wavelength .lambda.2PL" are
changed to a wavelength .lambda.2PL, and the wavelength
.lambda.3PR' and the wavelength .lambda.3PR" are changed to a
wavelength .lambda.3PR. Operations of a transmitting station 20 and
a receiving station 40 are similar to the operations of the
transmitting station 20 and the receiving station 40 in the optical
system 10c described in the first modification of the first
embodiment, descriptions of which are thus omitted. Only the inside
of the repeating station will be described.
[0359] FIG. 20 is a diagram showing an internal structure of a
first repeating station according to an eighth modification of the
first embodiment of this invention. A first repeating station 30h
shown in FIG. 20 comprises a first optical transmitting means and a
second optical transmitting means.
[0360] The first repeating station 30h comprises a first filter
31d, a first pumping source 66a, a first optical amplifier 31a and
an isolator 31c. They function in cooperation as a first optical
transmitting means. The first optical transmitting means receives
first transmission light (.lambda.1L) transmitted from a
transmitting station 20c (refer to FIG. 3) through the first
optical fiber and first pumping light (.lambda.2PL) and changes
either a level of the first transmission light (.lambda.1L) or a
level of the first pumping light (.lambda.2PL) to a necessary
level, amplifies the changed first transmission light (.lambda.1L)
and first pumping light (.lambda.2PL), and outputs second
transmission light (.lambda.1L') and second pumping light
(.lambda.2PL'). The first filter 31d is disposed on the input's
side of the first optical amplifier 31a to extract transmission
light (.lambda.1L, .lambda.1R) from a received optical signal, and
inputs the transmission light (.lambda.1L, .lambda.1R) to the first
optical amplifier 31a.
[0361] The first repeating station 30h comprises a second filter
33d, a second pumping source 64a, a second optical amplifier 33c
and an isolator 33a. They function in cooperation as a second
optical transmitting means. The second optical transmitting means
receives third transmission light (.lambda.1L) and third pumping
light (.lambda.3PR) transmitted from a receiving station 40c (refer
to FIG. 3) through the second optical fiber, changes either a level
of the third transmission light (.lambda.1R) or a level of the
third pumping light (.lambda.3PR) to a necessary level, amplifies
the changed third transmission light (.lambda.1R) and third pumping
light (.lambda.3PR), and outputs fourth transmission light
(.lambda.1R'). The second filter 33d is disposed on an input's side
of the second optical amplifier 33c to extract transmission light
(.lambda.1L, .lambda.1R) from a received optical signal, and inputs
the transmission light (.lambda.1L, .lambda.1R) to the second
optical amplifier 33c.
[0362] In FIG. 20, parts designated by like reference characters
have like or corresponding functions described above, further
descriptions of which are thus omitted. A second repeating station
30h' has a similar structure to that of the first repeating station
30h.
[0363] With this, transmission light (.lambda.1L+.lambda.2PL) from
the transmitting station 20c is inputted to the first repeating
station 30h. Only a .lambda.1L component of this inputted light is
extracted by the first filter 31d. This .lambda.1L component is
outputted as it is, multiplexed with .lambda.2PL from the first
pumping source 66a, and inputted to a first optical amplifier 31a.
The optical signal (.lambda.1L'+.lambda.2PL) optically amplified by
the first optical amplifier 31a is transmitted to the isolator 31c,
and sent as it is to the second repeating station 30h'.
[0364] With regard to inputted light (.lambda.1R'+.lambda.3PR) from
the second repeating station 30h', transmission light
(.lambda.1R"+.lambda.3P- R) is transmitted to the transmitting
station 20c.
[0365] The second repeating station 30h' (identical to the first
repeating station 30h) shown in FIG. 20 is similar. Namely,
transmission light (.lambda.1L'+.lambda.2PL) from the first
repeating station 30h (on the left side in FIG. 20) is inputted to
the second repeating station 30h'. Only a .lambda.1L' component of
this inputted light is extracted by a first filter 31d, and
outputted as it is. This component is multiplexed with .lambda.2PL
from a first pumping source 66a, and inputted to a first optical
amplifier 31a. The optical signal (.lambda.1R"+.lambda.2PL)
optically amplified by the first optical amplifier 31a is
transmitted to an isolator 31c, and sent as it is to the receiving
station 31c.
[0366] Inputted light (.lambda.1R+.lambda.3PR) from the receiving
station 40c is similar. An optical signal (.lambda.1R"+.lambda.3PR)
is transmitted to the first repeating station 30h.
[0367] As this, communication is performed among the stations using
only optical cables in only one system, and the output level of the
pumping source is automatically controlled in each of the stations,
which allows the optimum communication.
[0368] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect cut of the optical cable, thus reliability and safety of the
optical system 10c are remarkably improved.
[0369] (A9) Description of Ninth Modification of First Embodiment
of the Invention
[0370] Next, a disconnect detecting function additionally provided
to the structure of the repeating station shown in FIG. 20 will be
described. FIG. 21 is a diagram showing a structure of an optical
system 10g according to a ninth modification of the first
embodiment of this invention. In FIG. 21, detection of cut of an
optical cable between a transmitting station 20b and a first
repeating station 30i is performed such that a first transmitting
side monitoring means 26b in a transmitting station 20b monitors
residual pumping light .lambda.5PT from a first repeating station
30i, and determines that the optical cable is cut when the input
dies out. Between a receiving station 40b and a second repeating
station 30i' is similar. In the receiving station 40b, a first
receiving side monitoring means 46b monitors residual pumping light
.lambda.6PT from the second repeating station 30i', and determines
that the optical cable is cut when the input dies out. In FIG. 21,
parts designated by like reference characters have like or
corresponding functions described above, further descriptions of
which are thus omitted.
[0371] FIG. 22 is a diagram showing an internal structure of the
first repeating station 30i according to the ninth modification of
the first embodiment of this invention. The first repeating station
30i shown in FIG. 22 monitors inputted light from the transmitting
station 20b to detect cut by this monitoring function, as compared
with the first repeating station 30h (refer to FIG. 20).
[0372] A first disconnect detecting means 35' is almost the same as
the above first disconnect detecting means 35, but a wavelength
that the first disconnect detecting means 35' can detect differs.
Namely, the first disconnect detecting means 35' is disposed at an
entrance of the first optical fiber to detect cut of the first
optical fiber. The first disconnect detecting means 35' comprises a
seventh filter (filter 7) 35e, a fifth optical detector (photodiode
5) 35d, and a first disconnect detection outputting means 35c.
[0373] The seventh filter 35e extracts residual pumping light
(.lambda.2PL) from a received transmission light, and outputs it.
The fifth optical detector 35d detects residual pumping light
(.lambda.2PL) from the fifth filter 35e. The first disconnect
detection outputting means 35c monitors the operation of the fifth
optical detector 35d to output information relating to
presence/absence of the residual pumping light (.lambda.2PL). In
FIG. 22, parts designated by like reference characters have like or
coresponding functions described above, further descriptions of
which are thus omitted.
[0374] In the first repeating station 30i shown in FIG. 22,
inputted light (.lambda.1L+.lambda.2PL) from the transmitting
station 20b is branched into the three directions; toward a first
filter 31d, the first disconnect detecting means 35' and an
isolator 33a, using an optical coupler 50 (not shown) or the like.
Only .lambda.1L is inputted to the first filter 31d, multiplexed
with pumping light .lambda.4PT, inputted to a first optical
amplifier 31a, and transmitted along with residual pumping light to
the second repeating station 30i'.
[0375] The seventh filter 35e of the first disconnect detecting
means 35' extracts only residual pumping light .lambda.2PL of the
transmitting station 20b, and the fifth optical detector 35d
monitors its input, and determines that the optical cable between
the transmitting station 20b and the first repeating station 30i is
cut when the input dies out.
[0376] Transmission light (.lambda.1R"+.lambda.5PT) is sent to the
transmitting station 20b. When the optical cable between the
transmitting station 20b and the first repeating station 30i is
cut, the transmission light is returned as it is to the repeating
station 30. In this case, the level of .lambda.5PT does not fall,
and .lambda.1R" has the same wavelength as the transmission optical
signal .lambda.1L, so that they cannot be used as elements to
detect cut.
[0377] On the other hand, .lambda.2PL loses its supply source, thus
its level falls. For this, cut of the optical cable is detected
using .lambda.2PL. Inputted light from the second repeating station
30i' is similar.
[0378] FIG. 23 is a diagram showing an internal structure of the
second repeating station 30i' according to the ninth modification
of the first embodiment of this invention. In the second repeating
station 30i' shown in FIG. 23, disconnect detection similar to that
in the first repeating station 30i is performed.
[0379] A second disconnect detecting means 36' is similar to the
above second disconnect detecting means 36, but a wavelength that
the second disconnect detecting means 36' can detect is different.
Namely, the second disconnect detecting means 36' is disposed at
the entrance of a second optical fiber to detect cut of the second
optical fiber. The second disconnect detecting means 36' comprises
an eighth filter 36e, a sixth optical detector 36d and a second
disconnect detection outputting means 36c.
[0380] The eighth filter 36e extracts residual pumping light
(.lambda.3PR) from a received optical signal, and outputs it. The
sixth optical detector 36d detects the residual pumping light
(.lambda.3PR) from the eighth filter 36e. The second disconnect
detection outputting means 36c monitors the operation of the sixth
detector 36d, and outputs information relating to presence/absence
of the residual pumping light (.lambda.3PR). In FIG. 23, parts
designated by like reference characters have like or corresponding
functions, further descriptions of which are thus omitted.
[0381] With the above structure, inputted light
(.lambda.1L'+.lambda.4PT) from the first repeating station 30i is
branched into three directions; toward a first filter 31d, a first
disconnect detecting means 35' and an isolator 33a, by an optical
coupler 50 or the like (not shown). Only .lambda.1L' is inputted to
the first filter 31d, multiplexed with pumping light .lambda.6PT,
inputted to a first optical amplifier 31a, and transmitted along
with the residual pumping light to the receiving station 40b. A
seventh filter 35e of the first disconnect detecting means 35'
extracts only residual pumping light .lambda.4PT from the first
repeating station 30i, and a fifth optical detector 35d monitors
its input. When the input dies out, it is determined that the
optical cable between the first repeating station 30i and the
second repeating station 30i' is cut.
[0382] As shown in FIG. 22, transmission light
(.lambda.1R'+.lambda.7PT) is transmitted to the first repeating
station 30i. However, when the optical cable between the first
repeating station 30i and the second repeating station 30i' is cut,
this transmission light is returned as it is to the second
repeating station 30i'. In such case, since the level of
.lambda.7PT does not fall, and .lambda.1R' has the same wavelength
as a transmission light optical signal .lambda.1L from the
transmitting station 20b, they cannot be used as elements to detect
cut.
[0383] On the other hand, .lambda.4PT loses its supply source, thus
its level falls. By using this, cut of the optical cable is
detected. Inputted light from the receiving station 40b is
similar.
[0384] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect cut of the optical cable, thus reliability and safety of the
optical system 10g are remarkably improved.
[0385] (A10) Description of Tenth Modification of First Embodiment
of the Invention
[0386] FIG. 24 is a diagram showing a structure of an optical
system according to a tenth modification of the first embodiment of
this invention. An optical system 10h shown in FIG. 24 is similar
to the optical system described above. A controlling means 25 in a
transmitting station 20d' keep monitoring pumping light .lambda.5PT
from a first repeating station 30k at all times. When the reception
level falls, the controlling means 25 determines that an optical
cable between the transmitting station 20d' and the first repeating
station 30k is cut, controls a first pumping source 22d in
consideration of safety, and stops an output of the first pumping
source 22d if necessary. The receiving station 40d' is similar. In
FIG. 24, parts designated by like reference characters have like or
corresponding functions described above, further descriptions of
which are thus omitted.
[0387] FIG. 25 is a diagram showing an internal structure of the
first repeating station 30k according to the tenth modification of
the first embodiment of this invention. A first pumping light
controlling means (control unit) 66b controls an output of a first
pumping source (pumping source 1) 66a on the basis of a level of
first pumping light (.lambda.4PT) and a level of residual pumping
light (.lambda.4PT) in the second repeating station 30k'. A second
pumping light controlling means 64b controls an output of a second
pumping source 64a (pumping source 2) on the basis of a level of
second pumping light (.lambda.5PT) and a level of residual pumping
light (.lambda.5PT) in the transmitting station 20d'. In FIG. 25,
parts designated by like reference characters have like or
corresponding functions described above, further descriptions of
which are thus omitted.
[0388] FIG. 26 is a diagram showing an internal structure of the
second repeating station 30k' according to the tenth modification
of the first embodiment of this invention. The first pumping light
controlling means (control unit) 66b stops an output of a first
pumping source (pumping source 1) 66a when a reception level of
first pumping light (.lambda.3PR) falls, and a second pumping
source controlling means 64b stops an output of a second pumping
source 64a when a reception level of second pumping light
(.lambda.4PT) falls. In FIG. 26, parts designated by like reference
characters have like same or corresponding functions described
above, further descriptions of which are thus omitted.
[0389] In the first repeating station 30k shown in FIG. 25, a level
of a fifth optical detector 35d (photodiode 5) is always monitored
by the first pumping light controlling means 66b. when the
reception level falls (when cut is detected), the first pumping
light controlling means 66b stops an output of the first pumping
source 66a in consideration of safety.
[0390] Similarly, a level of a sixth optical detector 36d
(photodiode 6) is always monitored by the second pumping light
controlling means 64b. When the reception level falls, the second
pumping light controlling means 64b stops an output of the second
pumping source 64a in consideration of safety.
[0391] In the first repeating station 30k' shown in FIG. 26, a
level of the fifth optical detector 35d (photodiode 5) is always
monitored by the first pumping light controlling means 66b. When
the reception level falls, the first pumping light controlling
means 66b stops an output of the first pumping source 66a in
consideration of safety.
[0392] Similarly, a level of the sixth optical detector 36d
(photodiode 6) is always monitored by the second pumping light
controlling means 64b. When the reception level falls, the second
pumping light controlling means 64b stops an output of the second
pumping source 64a in consideration of safety.
[0393] As this, communication is performed among the stations using
only optical cables in one system, and the output level of the
pumping source is automatically controlled in each of the stations,
which allows the optimum communication. Safe optical transmission
becomes possible by the optical cable disconnect detecting
function.
[0394] (B) Description of Second Embodiment of the Invention
[0395] FIG. 27 is a diagram showing a structure of an optical
system according to a second embodiment of this invention. An
optical system 10i shown in FIG. 27 is a similar optical system to
those described above. Structures of a transmitting station 20f "
and a receiving station 40f " are equivalent to the transmitting
station 20f and the receiving station 40f shown in FIG. 16 to which
disconnect detecting means 26 and 46 are added, and a reflecting
means (reflecting element 1) 11a and a reflecting means (reflecting
element 2) 11b are disposed on outputs' side of isolators 22c and
42c, respectively. Each of these reflecting means 11a and 11b
reflects an optical signal at a specific wavelength contained in a
received optical signal, a specific wavelength reflecting element
such as a fiber grating or the like being used therefor. In FIG.
27, parts designated by like reference characters have like or
corresponding functions described above, further descriptions of
which are thus omitted.
[0396] FIG. 28 is a diagram showing an internal structure of a
first repeating station 70a according to the second embodiment of
this invention. A first repeating station 70a shown in FIG. 28
comprises a reflecting means (reflecting element 1) 11a at an
entrance leading to the transmitting station 20f". FIG. 29 is a
diagram showing an internal structure of a second repeating station
70a' according to the second embodiment of this invention. A second
repeating station 70a' is similar to the first repeating station
70a. In FIGS. 28 and 29, parts designated by like reference
characters have like or corresponding functions described above,
further descriptions of which are thus omitted.
[0397] The first repeating station 70a (refer to FIG. 28) comprises
a first disconnect detecting means 35', a second disconnect
detecting means 36', the reflecting means 11a, a first reflected
light receiving means 65, a reflecting means (reflecting element 2)
11b, and a second reflected light receiving means 64.
[0398] The first disconnect detecting means 35' is disposed on the
entrance's side of a first optical fiber to detect cut of the first
optical fiber. The first disconnect detecting means 35' comprises a
seventh filter (filter 7) 35e, a fifth optical detector (photodiode
5) 35d, and a first disconnect detection outputting means
(disconnect detection) 35c. The seventh filter 35e extracts
residual pumping light (.lambda.2PL) from a received optical
signal, and outputs it. The fifth optical detector 35d detects the
residual pumping light (.lambda.2PL) from the seventh filter 35e.
The first disconnect detection outputting means 35c monitors the
operation of the fifth optical detector 35d, and outputs
information relating to presence/absence of the residual pumping
light (.lambda.2PL).
[0399] The second disconnect detecting means 36' is disposed on the
entrance's side of a second optical fiber to detect cut of the
second optical fiber. The second disconnect detecting means 36'
comprises an eighth filter (filter 8) 36e, a sixth optical detector
(photodiode 6) 36d, and a second disconnect detection outputting
means (disconnect detection) 36c. The eighth filter 36e extracts
residual pumping light (.lambda.7PT) from a received optical
signal, and outputs it. The sixth optical detector 36d detects the
residual pumping light (.lambda.7PT) from the eighth filter 36e.
The second disconnect detection outputting means 36c monitors the
operation of the sixth optical detector 36d, and outputs
information relating to presence/absence of the residual pumping
light (.lambda.7PT).
[0400] The reflecting means 11a is disposed on the input's side of
a first optical amplifier 31a to reflect an optical signal
(.lambda.2PL) at a specific wavelength contained in a received
optical signal, a specific wavelength reflecting element such as a
fiber grating or the like being used therefor.
[0401] The first reflected light receiving means 65 is disposed on
the input's side of the first optical amplifier 31a to detect
residual pumping light (.lambda.5PT) contained in a received
optical signal, thereby detecting a level of the residual pumping
light (.lambda.5PT). The first reflected light receiving means 65
comprises a fifth filter (filter 5) 65a, and a third optical
detector (photodiode 3) 65b.
[0402] The fifth filter 65a is disposed on the input's side of the
first optical amplifier 31a to detect residual pumping light
(.lambda.5PT) contained in a received optical signal. The third
optical detector 65b detects a level of the residual pumping light
(.lambda.5PT) outputted from the fifth filter 65a.
[0403] The reflecting means 11b is disposed on the input's side of
a second optical amplifier 33c to reflect an optical signal
(.lambda.7PT) at a specific wavelength contained in the received
optical signal, a specific wavelength reflecting element such as a
fiber grating or the like being used therefor.
[0404] The second reflected light receiving means 64 is disposed on
the input's side of the second optical amplifier 33c to detect
residual pumping light (.lambda.4PT) contained in a received
optical signal, thereby detecting a level of the residual pumping
light (.lambda.4PT). The second reflected light receiving means 64
comprises a sixth filter (filter 6) 64a, and a second optical
detector (photodiode 2) 64b.
[0405] The sixth filter 64a is disposed on the input's side of the
second optical amplifier 33c to detect residual pumping light
(.lambda.4PT) contained in a received optical signal. The second
optical detector 64b detects a level of the residual pumping light
(.lambda.4PT).
[0406] Whereby, .lambda.5PT (pumping light inside the first
repeating station 70a, for amplifying a signal from the receiving
station 40f") is sent back to the first repeating station 70a by
the reflecting means 11a in the transmitting station 20f".
Similarly, .lambda.6PT (pumping light inside the second repeating
station 70a', for amplifying a signal from the transmitting station
20f") is sent back to the second repeating station 70a' by the
reflecting means 11b in the receiving station 40f".
[0407] To detect cut of the optical fiber between the transmitting
station 20f" and the first repeating station 70a, residual pumping
light .lambda.5PT from the first repeating station 70a is monitored
by the fifth filter 65a, and it is determined that the optical
cable is cut when the input dies out.
[0408] In the transmitting station 20f", a level of residual
pumping light .lambda.2PL reflected by the reflecting means 11a in
the first repeating station 70a is monitored by the second optical
detector 64b, an actual transmission loss between the transmitting
station 20f" and the first repeating station 70a is calculated, a
first pumping source 22d is adjusted by a controlling means 25 so
as to yield the optimum amplification factor, whereby the output
level to the first repeating station 70a is controlled.
[0409] In FIG. 28, inputted light
(.lambda.1L+.lambda.2PL+.lambda.5PT) from the transmitting station
20f" is branched into three directions; toward the reflecting means
11a, the fifth filter 65a and the seventh filter 35e, by an optical
coupler 50 or the like (not shown). A .lambda.2PL component of the
light toward the reflecting means 11a is reflected by the
reflecting means 11a, thus only (.lambda.1L+.lambda.5PT) components
are inputted to a first filter 31d. Only an optical signal
component .lambda.1L is extracted by the first filter 31d, and
multiplexed with pumping light .lambda.4PT. The multiplexed optical
component is inputted to the first optical amplifier 31a, and
transmitted along with residual pumping light to the second
repeating station 70a'.
[0410] In the second direction, only the residual pumping light
.lambda.5PT reflected by the reflecting means 11a in the
transmitting station 20f" is extracted by the fifth filter 65a, an
input level thereof is monitored by the third optical detector 65b.
This monitor value is read by a second pumping light controlling
means 64b, an actual transmission loss between the transmitting
station 20f" and the first repeating station 70a is calculated by a
second pumping light controlling means 64b, and a second pumping
source 64a is so adjusted as to yield the optimum amplification
factor. Whereby, the output level to the transmitting station 20f"
is controlled.
[0411] In the third direction, only the residual pumping light
.lambda.2PL of the transmitting station 20f" is extracted by the
seventh filter 35e, and an input thereof is monitored by the fifth
optical detector 35d. When the input dies out, it is determined
that the optical cable between the transmitting station 20f" and
the first repeating station 70a is cut.
[0412] In FIG. 29, between the receiving station 40f" and the
second repeating station 70a', the residual pumping light
.lambda.3PR from the receiving station 40f" is monitored by a sixth
optical detector 36d (photodiode 6), and it is determined that the
optical cable disconnects when the input goes out, as well.
[0413] Inputted light (.lambda.1L L'+.lambda.4PT+.lambda.7PT) from
the first repeating station 70a is branched into three directions;
toward a reflecting means 11a, a fifth filter 65a and a seventh
filter 35e, by an optical coupler 50 or the like (not shown).
[0414] In the first direction, only .lambda.4PT is reflected by the
reflecting means 11a, and only (.lambda.1L'+.lambda.7PT) components
are inputted to a first filter 31d. Only an optical signal
component .lambda.1L' is extracted by the first filter 31d,
multiplexed with pumping light .lambda.6PT, inputted to a first
optical amplifier 31a, and transmitted along with residual pumping
light to the receiving station 40f".
[0415] In the second direction, only the residual pumping light
.lambda.7PT reflected by the reflecting means 11b in the first
repeating station 70a is extracted by the fifth filter (filter 5)
65a, an input level thereof is monitored by the third optical
detector 65b, an actual transmission loss between the first
repeating station 70a and the second repeating station 70a' is
calculated, a second pumping source 64a is adjusted by the second
pumping source controlling means 64b so as to yield the optimum
amplification factor, whereby the output level to the first
repeating station 70a is controlled.
[0416] In the third direction, only the residual pumping light
.lambda.4PT in the first repeating station 70a is extracted by the
seventh filter (filter 7) 35e, the input thereof is monitored by
the fifth filter 65a. When the input dies out, it is determined
that the optical fiber between the first repeating station 70a and
the second repeating station 70a' is cut.
[0417] With the above structure, transmission light to the
transmitting station 20f" has three components; .lambda.1R",
.lambda.5PT and .lambda.2PL, and they are returned as they are when
the optical cable between the transmitting station 20f" and the
first repeating station 70a is cut. In such case, a level of
.lambda.5PT does not fall and .lambda.1R" is at the same wavelength
as the transmission optical signal .lambda.1L from the transmitting
station 20f", hence they can not be used as detecting elements to
detect cut.
[0418] On the other hand, .lambda.2PL loses its supply source, and
its level falls. By detecting disconnection of inputs of
.lambda.2PL, it is possible to detect cut of the optical cable.
Incidentally, inputted light from the first repeating station 70a
is similar.
[0419] By inserting the specific wavelength reflecting elements
(reflecting means 11a and 11b), it is possible to calculate an
actual transmission loss between the stations irrespective of a
gain control in the opposite station, and a gain control on the
transmission light suitable for it becomes possible.
[0420] In FIG. 29, transmission light to the first repeating
station 70a has .lambda.1R', .lambda.7PT and .lambda.4PT, and they
are returned as they are to the second repeating station 70a' when
the optical cable between the first repeating station 70a the
second repeating station 70a' is cut. In such case, the level of
.lambda.7PT does not fall, and .lambda.1R' is at the same
wavelength as the optical signal .lambda.1L' from the first
repeating station 70a, thus they cannot be used as detecting
elements to detect cut. On the other hand, .lambda.4PT loses its
supply source, thus its level falls. By detecting disconnection of
the inputs of .lambda.4PT, it is possible to detect cut of the
optical cable. Incidentally, inputted light from the receiving
station 40f" is similar.
[0421] As above, communication is performed among the stations
using only the optical cables in one system, and the output level
of the pumping source is automatically controlled in each of the
stations, which allows the optimum communication.
[0422] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect cut of the optical cable, so that reliability and safety of
the optical system 10i is remarkably improved.
[0423] (B1) Description of First Modification of Second Embodiment
of the Invention
[0424] FIG. 30 is a diagram showing a structure of an optical
system according to a first modification of the second embodiment
of this invention. An optical system 10j shown in FIG. 30 is
similar to that described above. A transmitting station 20a" and a
receiving station 40a" shown in FIG. 30 are similar to the
transmitting station 20a and the receiving station 40a described in
the second modification (refer to FIG. 5) of the first embodiment.
In the transmitting station 20a, a reflecting means (reflecting
element 1) 11a is provided on the output's side of the optical
amplifier 22b. In the receiving station 40a, a reflecting means
(reflecting element 2) 11b is provided on the output's side of the
optical amplifier 42b.
[0425] FIG. 31 is a diagram showing an internal structure of a
first repeating station 70b according to the first modification of
the second embodiment of this invention. FIG. 32 is a diagram
showing an internal structure of a second repeating station 70b'
according to the first modification of the second embodiment of
this invention. The stations shown in FIGS. 31 and 32 are similar
to those shown in FIGS. 28 and 29, respectively, in each of which
monitoring means are provided on the outputs' side of a first
optical amplifiers 31a and a second optical amplifier 33c. The
first repeating station 70b comprises a second filter (filter 2)
37a, a first optical detector (photodiode 1) 37b, a fourth filter
(filter 4) 67a and a fourth optical detector (photodiode 4)
67b.
[0426] The second filter 37a is disposed on the output's side of
the first optical amplifier 31a to extract first pumping light
(.lambda.4PT), and outputs it. The first optical detector 37b
displays a level of a first transmission light (.lambda.4PT)
outputted from the second filter 37a. The fourth filter 67a is
disposed on the output's side of the second optical amplifier 33c
to extract second pumping light (.lambda.5PT), and outputs it. The
fourth optical detector 67b displays a level of the second
transmission light (.lambda.5PT) extracted by the fourth filter
67a.
[0427] Namely, the first repeating station 70b comprises the second
filter 37a disposed on the output's side of the first optical
amplifier 31a to extract the first pumping light (.lambda.4PT) and
output it, the first optical detector 37b displaying a level of the
first transmission light (.lambda.4PT) outputted from the second
filter 37a, the fourth filter 67a disposed on the output's side of
the second optical amplifier 33c to extract the second pumping
light (.lambda.5PT) and output it, and a fourth optical detector
67b displaying a level of the second transmission light
(.lambda.5PT) extracted by the fourth filter 67a.
[0428] In FIGS. 30 and 31, parts designated by like reference
characters have like or corresponding functions described above,
further descriptions of which are thus omitted.
[0429] Inputted light (.lambda.1L+.lambda.2PT +.lambda.5PT) from
the transmitting station 20a" is branched into three directions;
toward a reflecting means 11a, a fifth filter 65a and a seventh
filter 35e, by an optical coupler 50 or the like (not shown).
[0430] Since the reflecting means 11a reflects only .lambda.2PT,
only (.lambda.1L+.lambda.5PT) components are inputted to a first
filter 31d. Only an optical signal component .lambda.1L is
extracted by the first filter 31d, multiplexed with pumping light
.lambda.4PT, inputted to the first optical amplifier 31a, and
transmitted along with residual pumping light to the second
repeating station 70c.
[0431] The residual pumping light .lambda.5PT reflected by the
reflecting means 11a in the transmitting station 20a" is extracted
by the fifth filter 65a, and an input level thereof is monitored by
a third optical detector 65b.
[0432] Only the residual pumping light .lambda.2PL of the
transmitting station 20a" is extracted by the seventh filter 35e,
and an input thereof is monitored by a fifth optical detector 35d.
When the input dies out, it is determined that the optical cable
between the transmitting station 20a" and the first repeating
station 70b is cut. Transmission light to the transmitting station
20a" has (.lambda.1R"+.lambda.5PT+.lambda.2PL) components. When the
optical cable between the transmitting station 20a" and the first
repeating station 70b is cut, these components are returned as they
are to the first repeating station 70b. In which case, a level of
.lambda.5PT does not fall, and .lambda.1R" is at the same
wavelength as the transmission optical signal .lambda.1L from the
transmitting station 20a", hence they cannot be used as detecting
elements to detect cut.
[0433] On the other hand, .lambda.2PL loses its supply source, and
its level falls. Accordingly, by detecting disconnection of inputs
of .lambda.2PL, it is possible to detect cut of the optical cable.
When an input of .lambda.7PT dies out, it is determined that the
optical cable is cut, as well as inputted light from the second
repeating station 70b'.
[0434] In the second repeating station 70b' shown in FIG. 32,
inputted light (.lambda.1L'+.lambda.4PT +.lambda.7PT) from the
first repeating station 70b is branched into three directions;
toward a reflecting means 11a, a fifth filter 65a and a seventh
filter 35e, by an optical coupler 50 or the like (not shown).
[0435] The reflecting means 11a reflects only .lambda.4PT, thus
only (.lambda.1L'+.lambda.7PT) components are inputted to a first
filter 31d. Only an optical signal component .lambda.1L' is
extracted by the first filter 31d, multiplexed with pumping light
.lambda.6PT, inputted to the first optical amplifier 31a, and
transmitted along with residual pumping light to the receiving
station 40a".
[0436] Only the residual pumping light .lambda.7PT reflected by the
reflecting means 11b in the first repeating station 70b is
extracted by the fifth filter 65a, and an input level thereof is
monitored by a third optical detector 65b.
[0437] Only the residual pumping light .lambda.4PT of the first
repeating station 70b is extracted by the seventh filter 35e, and
input thereof is monitored by a fifth optical detector 35d. When
the input dies out, it is determined that the optical cable between
the first repeating station 70b and the second repeating station
70c is cut.
[0438] Transmission light to the first repeating station 70b has
(.lambda.1R'+.lambda.7PT+.lambda.4PT) components. When the optical
cable between the first repeating station 70b and the second
repeating station 70c is cut, the transmission light are returned
as it is to the second repeating station 70c. In which case, the
level of .lambda.7PT does not fall, and .lambda.1R' is at the same
wavelength as the transmission optical signal .lambda.1L' from the
first repeating station 70b, hence they cannot be used as detecting
elements to detect cut.
[0439] On the other hand, .lambda.4PT loses its supply source, thus
the level thereof falls. Accordingly, by detecting disconnection of
inputs of .lambda.PT, it is possible to detect cut of the optical
cable. Inputted light from the receiving station 40a" is
similar.
[0440] With the above structure in FIG. 30, .lambda.5PT (pumping
light for amplifying a signal from the receiving station 40a",
inside the first repeating station 70b) is looped back by the
reflecting means 11a in the transmitting station 20a" to the first
repeating station 70b. Similarly, .lambda.6PT (pumping light for
amplifying a signal from the transmitting station 20a", inside the
second repeating station 70b") is looped back to the second
repeating station 70b" by the reflecting means 11b in the receiving
station 40a".
[0441] Residual pumping light .lambda.5PT from the first repeating
station 70b is kept to be monitored by a fifth optical detector
35d. When input thereof dies out, it is determined that the optical
cable between the transmitting station 20a" and the first repeating
station 70b is cut.
[0442] Residual pumping light .lambda.6PT from the second repeating
station 70b' is kept to be monitored by a sixth optical detector
36d between the receiving station 40a" and the second repeating
station 70b', as well. When input thereof dies out, it is
determined that the optical cable is cut.
[0443] As this, since an amplified optical level is determined from
not a theoretical value but a measured value, a more accurate gain
control becomes possible. Communication is performed among the
stations using only optical cables in one system, and the output
level of the pumping source is automatically controlled in each of
the stations, which allows the optimum communication.
[0444] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect cut of the optical cable, which allows reliability and
safety of the optical system 10j to be remarkably improved.
[0445] (B2) Description of Second Modification of Second Embodiment
of the Invention
[0446] FIG. 33 is a diagram showing a structure of a first
repeating station according to a second modification of the second
embodiment of this invention. A first repeating station 70c (and a
second repeating station 70c') shown in FIG. 33 performs a
transmission level control between the stations. As the disconnect
detecting method, a relationship of fluctuations in output level of
a first pumping source 66a is confirmed, then cut of the optical
cable is determined. Incidentally, the optical system according to
this modification is identical to the optical system 10i shown in
FIG. 27.
[0447] The first repeating station 70c (or the second repeating
station 70c') comprises a reflecting means (reflecting element 1)
11a, a fifth filter (filter 5) 65a, a third optical detector
(photodiode 3) 65b, a seventh filter (filter 7) 35e, a fifth
optical detector (photodiode 5) 35d, a reflecting means (reflecting
element 2) 11b, a sixth filter (filter 6) 64a, a second optical
detector (photodiode 2) 64b, an eighth filter (filter 8) 36e, and a
sixth optical detector (photodiode 6) 36d.
[0448] The reflecting means 11a is disposed on the input's side of
a first filter 31d to reflect light at a specific wavelength
contained in a received optical signal. The fifth filter 65a
extracts residual pumping light (.lambda.5PT) from an optical
signal from an optical transmitting apparatus's side (refer to the
transmitting station 20f" in FIG. 27), and outputs it. The third
optical detector 65b detects the residual pumping light
(.lambda.5PT) from the fifth filter 65a.
[0449] The seventh filter 35e extracts residual pumping light
(.lambda.2PL) from an optical signal from the optical transmitting
apparatus's side, and outputs it. The fifth optical detector 35d
detects the residual pumping light (.lambda.2PL) outputted from the
filter 35e. The reflecting means 11b is disposed on the input's
side of a filter 33d to reflect light at a specific wavelength.
[0450] The sixth filter 64a extracts residual pumping light
(.lambda.4PT) from an optical signal from the optical receiving
apparatus's side, and outputs it. The second optical detector 64b
detects the residual pumping light (.lambda.4PT) from the filter
64a. The eighth filter 36e extracts residual pumping light
(.lambda.7PT) from an optical signal from the optical receiving
apparatus's side, and outputs it. The sixth optical detector 36d
detects the residual pumping light (.lambda.7PT) outputted from the
eighth filter 36e.
[0451] In FIG. 33, parts designated by like reference characters
have like or corresponding functions described above, further
descriptions of which are thus omitted.
[0452] Flows of operations of the first pumping source 66a and a
first pumping light controlling means 66b are as follows.
Incidentally, the second pumping light controlling means 64b is
similar.
[0453] First, a level of reception light of the second optical
detector 64b is detected, and a reception level of the sixth
optical detector 36d is monitored.
[0454] While cut is not detected, the reception level of the sixth
optical detector 36d is constant, an actual transmission loss
between the first repeating station 70c and the second repeating
station 70c' is calculated on the basis of an input level of the
second optical detector 64b, and the first pumping source 66a is
such controlled as to yield the optimum optical amplified
output.
[0455] When cut is detected, the reception level of the sixth
optical detector 36d falls, which causes fluctuation in bias
current or the like of the first pumping source 66a. This
fluctuation causes fluctuation in output level of the pumping light
.lambda.4PT. For this, a relationship between the fluctuation in
optical level (optical level reflected by a cross section of the
optical fiber and returned) detected by the second optical detector
64b and the fluctuation in pumping light output level is confirmed,
then it is determined that the optical cable disconnects.
[0456] With the above structure, an example of operation of the
first pumping light controlling means 66b is as described in (r1)
through (r3) below. Incidentally, the second pumping light
controlling means 64b is similar.
[0457] (r1) A level of reception light of the second optical
detector 64b is detected, and a reception level of the sixth
optical detector 36d is kept monitored.
[0458] (r2) When the reception level of the sixth optical detector
36d is constant (while cut is not detected) an actual transmission
loss between the first repeating station 70c and the second
repeating station 70c' is calculated on the basis of an input level
of the second optical detector 64b, and the first pumping source
22d is such controlled as to yield the optimum optical amplified
output.
[0459] (r3) When the reception level of the sixth optical detector
36d falls (when cut is detected), the bias current or the like of
the first pumping source 22d is fluctuated, whereby the output
level of the pumping light .lambda.4PT is fluctuated. Therefore, a
relationship between the fluctuation in optical level (optical
level reflected by a cross section of the optical cable and
returned) detected by the second optical detector 64b and the
fluctuation in pumping light output level is confirmed, cut of the
optical cable is then detected.
[0460] As this, after a relationship of fluctuation in output level
of the first pumping source 66a is confirmed, cut of the optical
cable is determined, and the control is performed by calculating an
amplified optical level with a theoretical value. This allows an
accurate control.
[0461] (B3) Description of Third Modification of Second Embodiment
of the Invention
[0462] FIG. 34 is a diagram showing a structure of an optical
system according to a third modification of the second embodiment
of this invention. An optical system 10k shown in FIG. 34 comprises
a transmitting station 20g, a first repeating station 70d, a second
repeating station 70d' and a receiving station 40g. The optical
system 10k is equivalent to the optical system 10i (refer to FIG.
27) in which an output monitoring function is additionally provided
to the transmitting side and the receiving side.
[0463] FIG. 35 is a diagram showing an internal structure of the
first repeating station 70d (or the second repeating station 70d')
according to the third modification of the second embodiment of
this invention.
[0464] The first repeating station 70d comprises a second filter
(filter 2) 37a, a first optical detector (photodiode 1) 37b, a
fourth filter (filter 4) 67a, and a fourth optical detector
(photodiode 4) 67b. The second filter 37a is disposed on the
output's side of a first optical amplifier 31a to extract first
pumping light (.lambda.4PT) outputted from the first optical
amplifier 31a. The first optical detector 37b detects a level of
the first pumping light (.lambda.4PT) outputted from the second
filter 37a. The fourth filter 67a is disposed on the output's side
of a second optical amplifier 33c to extract second pumping light
(.lambda.5PT) outputted from the second optical amplifier 33c. The
fourth optical detector 67b detects a level of the second pumping
light (.lambda.5PT) outputted from the fourth filter 67a.
[0465] The eighth filter (filter 8) 36e extracts residual pumping
light (.lambda.7PT) from a received optical signal, and outputs it.
A sixth optical detector (photodiode 6) 36d detects the residual
pumping light (.lambda.7PT) from the eighth filter 36e. An output
level of the first optical amplifier 31a is controlled on the basis
of a detected level of the first optical detector 37b, a detected
level of the second optical detector 64b and a detected level of
the sixth optical detector 36d.
[0466] A seventh filter (filter 7) 35e extracts residual pumping
light (.lambda.2PT) from a received optical signal, and outputs it.
The fifth optical detector (photodiode 5) 35d detects the residual
pumping light (.lambda.2PT) from the seventh filter 35e. An output
level of the second optical amplifier 33c is controlled on the
basis of a detected level of the fourth optical detector
(photodiode 4) 67b, a detected level of a third optical detector
65b and a detected level of the fifth optical detector 35d.
[0467] In FIGS. 34 and 35, parts designated by like reference
characters have like or corresponding functions described above,
further descriptions of which are thus omitted.
[0468] With the above structure, the control is performed as
described in (r4) through (r6) below. Incidentally, although the
following is a case of the first pumping light controlling means
66b, a case of the second pumping light controlling means 64b is
similar.
[0469] (r4) A difference in reception light level between the first
optical detector (photodiode 1) 37b and a second optical detector
(photodiode 2) 64b is detected. A reception level of the sixth
optical detector 36d is monitored.
[0470] (r5) when the reception level of the sixth optical detector
36d is constant (while cut is not detected), an actual transmission
loss between the first repeating station 70d and the second
repeating station 70d' is calculated on the basis of (r4), and the
first pumping source 22d in the transmitting station 20g is such
controlled as to yield the optimum optical amplified output.
[0471] (r6) When the reception level of the sixth optical detector
36d falls (while cut is detected), the bias current or the like of
a first pumping source 66a is fluctuated, whereby the output level
of the pumping light .lambda.4PT is fluctuated. After a
relationship between the fluctuation in optical level (optical
level reflected by a cross section of the optical cable and
returned) of the second optical detector 64b and the fluctuation in
output level of the pumping light is confirmed, cut of the optical
cable is determined.
[0472] As this, a more accurate gain control is possible by
determining an amplified optical level in actual measurement.
[0473] As this, communication among the stations is performed using
only the optical cables in one system, and the output level of the
pumping source is automatically controlled in each of the stations,
which allows the optimum communication.
[0474] In the above manner, the installation cost and maintenance
cost of the optical cables are largely decreased, and each of the
stations can detect cut of the optical cable, which allows
reliability and safety of the optical system to be remarkably
improved.
[0475] (C) Description of Third Embodiment of the Invention
[0476] FIG. 36 is a diagram showing a structure of an optical
system according to a third embodiment of this invention. An
optical system 10L shown in FIG. 36 comprises a transmitting
station 20h, a first repeating station 70c, a second repeating
station 70c' and a receiving station 40h. The optical system 10L is
equivalent to the optical system 10i (refer to FIG. 27) in which an
output monitoring function is added to the transmitting side and
the receiving side.
[0477] In this modification, an alarm signal is sent to a
transmission path by modulating a pumping source, returning of the
alarm signal is confirmed, then cut of the optical cable is
determined.
[0478] FIG. 37 is a diagram showing a structure of the first
repeating station according to the third embodiment of this
invention. In the first repeating station 70c shown in FIG. 37, a
unit for superimposing a modulation signal as an alarm signal and
transmitting it is added to the first repeating station 70c shown
in FIG. 33. The first repeating station 70c comprises a first alarm
signal communication controlling means 69b, first optical switches
71c and 71d, a first alarm signal detecting means 68a, a second
disconnect detecting means 68b, a second alarm signal communication
controlling means 69a, second optical switches 71a and 71b, a
second alarm signal detecting means 68c, and a fourth disconnect
detecting means 68d.
[0479] The first alarm signal communication controlling means 69b
outputs a port switching signal in order to superimpose a
modulation signal on a second pumping source 64a and output it when
detecting that residual pumping light (.lambda.2PL) is not inputted
to the fifth optical detector 35d. The first optical switches 71c
and 71d are connected to the second pumping source 64a to select
according to the port switching signal outputted from the first
alarm signal communication controlling means 69b whether second
pumping light (.lambda.5PL) from the second pumping source 64a is
led to the input's side of a second optical amplifier 33c or the
second pumping light (.lambda.5PL) on which the modulation signal
has been superimposed is led to the output's side of the second
optical amplifier 33c. The first alarm signal detecting means 68a
is connected to a third optical detector 65b to detect the second
pumping light (.lambda.5PL), on which modulation signal has been
superimposed, looped back and inputted from the optical
transmitting apparatus's side (the transmitting station 20h in FIG.
36), and outputs a first alarm signal to the outside. The second
disconnect detecting means 68b detects that the first alarm signal
is outputted from the first alarm signal detecting means 68a. The
second alarm signal communication controlling means 69a outputs a
port switching signal in order to superimpose a modulation signal
on the first pumping source 66a and output it when detecting that
residual pumping light (.lambda.7PT) is not inputted to a sixth
optical detector 36d.
[0480] The second optical switches 71a and 71b are connected to a
first pumping source 66a to select according to a port switching
signal outputted from the second alarm signal communication
controlling means 69a whether first pumping light (.lambda.4PT)
from the first pumping source 66a is led to the input's side of a
first optical amplifier 31a or the first pumping light
(.lambda.4PT) on which the modulation signal has been superimposed
is led to the output's side of the first optical amplifier 31a. The
second alarm signal detecting means 68c is connected to a second
optical detector 64b to detect the first pumping light
(.lambda.4PT), on which the modulation signal has been
superimposed, looped back and inputted from the optical receiving
apparatus's side, and outputs a second alarm signal to the outside.
The fourth disconnect detecting means 68d detects that the second
alarm signal is outputted from the second alarm signal detecting
means 68c.
[0481] In FIGS. 36 and 37, parts designated by like reference
characters have like or corresponding functions described above,
further descriptions of which are thus omitted.
[0482] With the above structure, in the transmitting station 20h, a
level of reception light (light of pumping light .lambda.2PL of its
own station, returned from the first repeating station 70c) of the
second optical detector 64b is detected in the normal state, an
actual transmission loss between the transmitting station 20h and
the first repeating station 70c is calculated, and a first pumping
source 22d is such controlled as to yield the optimum optical
amplified output. The reception level of the fifth optical detector
35d is monitored.
[0483] When the reception level of the fifth optical detector 35d
is constant, cut is not detected. For this, the above operation is
performed. When the reception level of the fifth optical detector
35d falls (while cut is detected), an alarm signal communication
control unit 13 (in the transmitting station 20h) controls optical
switches 12a and 12b to switch a route {circle over (1)} in the
normal state to a route {circle over (2)}, modulates the pumping
source 22d, and transmits an alarm signal in a specific pattern to
the first repeating station 70 along the route {circle over
(2)}.
[0484] An alarm signal detecting unit 26d monitors whether the
alarm signal is inputted to the second optical detector 64b. When
the optical cable is cut, the light is reflected by the cross
section, and a modulated pumping light alarm signal is returned to
its own station. Whereby, disconnection of the optical signal is
determined when the alarm signal is detected.
[0485] The second repeating station 70c' (similar to that shown in
FIG. 37, although the detailed drawing is not shown) is similar.
Inputted light (.lambda.1L'+.lambda.4PT+.lambda.7PT) from the first
repeating station 70c is branched into three directions; toward a
reflecting means 11a, a fifth filter 65a and a seventh filter 35e,
by an optical coupler 50 or the like (not shown).
[0486] The reflecting means 11a reflects only .lambda.4PT, and only
(.lambda.1 L'+.lambda.7PT) components are inputted to a first
filter 31d. Only an optical signal component .lambda.1L' is
extracted by the first filter 31d, multiplexed with pumping light
.lambda.6PT, inputted to a first optical amplifier 31a, then
transmitted along with residual pumping light to the receiving
station 40h.
[0487] An actual transmission loss between the second repeating
station 70c' and the receiving station 40h is calculated from
returned pumping light .lambda.6PT from the receiving station 40h
(monitored by a second optical detector 64b), and an output of a
first pumping source 66a is such controlled by a first pumping
light controlling means 66b that the output becomes optimum. Only
the residual pumping light .lambda.7PT reflected by the reflecting
means 11a in the first repeating station 70c is extracted by the
fifth filter 65a, the input level is monitored by a third optical
detector 65b, an actual transmission loss between the first
repeating station 70c and the second repeating station 70c' is
calculated by the second pumping light controlling means 64b, and
an output of the second pumping source 64a is controlled to be
optimum.
[0488] Only the residual pumping light .lambda.4PT of the first
repeating station 70c is extracted by the seventh filter 35e, and
an input thereof is monitored by a fifth optical detector 35d. When
the input dies out, an alarm signal communication control unit 69b
controls optical switches 71c and 71d, switches a port P1 in the
normal state to a port P2 to modulate the pumping light, and
transmits an alarm signal in a specific pattern to the first
repeating station 70c from the port P2.
[0489] On the other hand, an alarm signal detecting unit 68a
monitors whether the alarm signal is inputted to the third optical
detector 65b. When the optical cable is cut, the alarm signal
obtained by modulating the pumping light is reflected by the cross
section, and returned to its own station. After detection of the
alarm signal is confirmed, it is determined that the optical cable
is cut.
[0490] As this, communication is performed among the stations using
only the optical cables in one system, and the output level of the
pumping source is automatically controlled, which allows the
optimum communication.
[0491] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the station scan
detect cut of the optical cable. This largely improves reliability
and safety of the optical system 10b.
[0492] (C1) Description of First Modification of Third Embodiment
of the invention
[0493] FIG. 38 is a diagram showing a structure of an optical
system according to a first modification of the third embodiment of
this invention. An optical system 10n shown in FIG. 38 comprises a
transmitting station 20i, a first repeating station 70d, a second
repeating station 70d' and a receiving station 40i. FIG. 39 is a
diagram showing an internal structure of the first repeating
station 70d according to the first modification of the third
embodiment of this invention. This modification is that a function
of modulating pumping light, sending an alarm signal to the
transmission path, confirming returning of it, and determining cut
of the optical cable is added to the above third embodiment.
[0494] There are provided a second filter (filter 3) 32b disposed
on the output's side of a first optical amplifier 31a to extract
first pumping light (.lambda.4PT) outputted from the first optical
amplifier 31a, a first optical detector (photodiode 1) 32c
detecting a level of the fist pumping light (.lambda.4PT) outputted
from the second filter 32b, a fourth filter (filter 4) 34a disposed
on the output's side of a second optical amplifier 33c to extract
second pumping light (.lambda.5PT) outputted from the second
optical amplifier 33c, and a fourth optical detector (photodiode 4)
34c detecting a level of the second pumping light (.lambda.5PT)
outputted from the fourth filter 34a.
[0495] In FIG. 38, parts designated by like reference character
have like or corresponding functions described above, further
descriptions of which are thus omitted.
[0496] With the above structure, the transmitting station 20i
(refer to FIG. 38) detects a difference in reception light level
between a first optical detector (photodiode 1) 23b and a second
optical diode (photodiode 2) 24b, calculates an actual transmission
loss between the transmitting station 20i and the first repeating
station 70d, and such controls a first pumping source 22d as to
yield the optimum optical amplified output. A reception level of a
fifth optical detector 26b (photodiode 5, corresponding to the
first transmitting side monitoring means 26b in FIG. 5) is
monitored. When the reception level of the fifth optical detector
26b is constant, cut is not detected. Accordingly, the above
operation is performed. When the reception level of the fifth
optical detector 26b falls (while cut is detected), an alarm signal
communication control unit 13 controls optical switches 12a and 12b
to switch a route {circle over (1)} in the normal state to a route
{circle over (2)}, modulates pumping light, and transmits an alarm
signal in a specific pattern to the first repeating station 70d
along the route {circle over (2)}.
[0497] An alarm signal detecting unit 26d monitors whether the
alarm signal is inputted to the second optical detector 24b. When
the optical cable is cut, the alarm signal obtained by modulating
the pumping light is reflected by the cross section, and returned
to its own station, thus cut of the optical cable is determined
after detection of the alarm signal is confirmed.
[0498] In FIG. 39, inputted light
(.lambda.1L+.lambda.2PL+.lambda.5PT) from the transmitting station
20i is branched into three directions; toward a reflecting means
11a, a fifth filter 65a and a seventh filter 35e, by an optical
coupler 50 or the like (not shown). Since the reflecting means 11a
reflects only .lambda.2PL, only (.lambda.1L+.lambda.5PT) components
are inputted to a first filter 31d. An optical signal component
.lambda.1L is extracted by the first filter 31d, multiplexed with
pumping light .lambda.4PT, inputted to the first optical amplifier
31a, and transmitted along with residual pumping light to the
second repeating station (not shown).
[0499] At this time, only a .lambda.4PT component is extracted by a
sixth filter 64a, a level of the .lambda.4PT light is monitored by
a second optical detector 64b, an actual transmission loss between
the first repeating station 70d and the second repeating station is
calculated on the basis of a difference in level between it and
returned pumping light .lambda.4PT (monitored by the second optical
detector 64b) from the second repeating station, and a first
pumping light controlling means 66b such controls that an output of
a first pumping source 66a become optimum.
[0500] A fifth filter 35a extracts only residual pumping light
.lambda.5PT reflected by a reflecting means 11a in the transmitting
station 20i, a third optical detector 65b monitors an input level
thereof, the second pumping light controlling means 64b calculates
an actual transmission loss between the transmitting station 20i
and the first repeating station 70d, and an output of a second
pumping source 64a is controlled to be optimum.
[0501] The seventh filter 35e extracts only residual pumping light
.lambda.2PL of the transmitting station 20i, and a fifth optical
detector 35d monitors an input of the residual pumping light
.lambda.2PL. When the input dies out, an alarm signal communication
control unit 32d controls optical switches 12a and 12b to switch a
port P1 in the normal state to a port 2, modulates the pumping
light, and transmits an alarm signal in a specific pattern to the
second repeating station. An alarm signal detecting unit 68c
monitors whether the alarm signal is inputted to the second optical
detector 64b. When the optical cable is cut, the light is reflected
by the cross section, and the alarm signal that is the modulated
pumping light is returned to its own station. It is thereby
determined that the cut is detected.
[0502] As this, communication is performed among the stations using
only the optical cables in one system, and the output level of the
pumping source is automatically controlled, which allows the
optimum communication.
[0503] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect disconnect of the optical cable. This largely improves
reliability and safety of the optical system 10n.
[0504] (C2) Description of Second Modification of Third Embodiment
of the Invention
[0505] FIG. 40 is a diagram showing a structure of an optical
system according to a second modification of the third embodiment
of this invention. An optical system 10p shown in FIG. 40
collectively amplifies optical signals at multiple wavelength, and
transmits them (hereinafter referred as a multiple wavelength
collective amplification system, occasionally), which comprises a
transmitting station 20j, a first repeating station 70b, a second
repeating station 70b' and a receiving station 40j. A difference
from the above first modification of the third embodiment is that
this modification is required to select a wavelength of each
pumping light because of the multiple wavelength collective
amplification system.
[0506] Each of the transmitting station 20j and the receiving
station 40j has multiplexing and demultiplexing functions for
multiple wavelength collective amplification along with the
functions of the transmitting station 20a" and the receiving
station 40a" (refer to FIG. 30) described above. Namely, the
transmitting station 20j comprises an optical coupler 51c, and a
plurality of transmitting units 28 as an optical transmitting means
75. Here, n is an integer. Each of the plural transmitting units 28
named a transmitting unit 1 (.lambda.1), a transmitting unit 2
(.lambda.2), . . . , and a transmitting unit n (.lambda.n) has the
same function as the above transmitting unit 22a. The optical
coupler 50c is connected to the plural transmitting units 28 and an
optical amplifier 22b to collectively amplify optical signals at
multiple wavelengths sent from the plural transmitting units 28,
and sends them.
[0507] The transmitting station 20j further comprises an optical
demultiplexer 14a and receiving units 21a-1, 21a-2, . . . , and
21a-n, as an optical receiving means 21e. The optical demultiplexer
14a selects reception light containing optical signals at multiple
wavelengths for each wavelength, and outputs it. Receiving unit 1
(.lambda.1), a receiving unit 2 ( (.lambda.2), . . . , a receiving
unit n (.lambda.n) represent the receiving units 21a-1, 21a-2, . .
. and 21a-n, respectively, each of which has the same function as
the above receiving unit 21a.
[0508] The receiving station 40j comprises a plurality of
transmitting units 48 and an optical coupler 51c, as an optical
transmitting means 76, to be able to collectively amplify optical
signals at multiple wavelengths, and sent them. Each of the plural
transmitting units 48 named a transmitting unit 1 (.lambda.1), a
transmitting unit 2 (.lambda.2), . . . , and a transmitting unit n
(.lambda.n) has the same function as the above transmitting unit
42a. The receiving station 40j further comprises an optical
demultiplexer 14b and receiving units 41a-1, 41a-2, . . . , and
41a-n each of which has the same function as the receiving unit 41b
(refer to FIG. 1), as an optical receiving means 41e to be able to
select reception light at each wavelength contained in an optical
signal at multiple wavelengths, and output it.
[0509] Incidentally, the first repeating station 70b and the second
repeating station 70b' are almost the same as those described in
the first modification (refer to FIG. 31) of the second embodiment
of this invention, but monitor different wavelengths. In FIG. 40,
parts designated by like character have like or corresponding
functions described above, further descriptions of which are thus
omitted.
[0510] Wavelengths of transmission light of the transmitting
station 20j are .lambda.1 to .lambda.n (n being an integer), which
are multiplexed in one optical cable by the optical coupler 51c,
collected into an optical signal at a wavelength .lambda.L,
multiplexed with a pumping source (not shown) having a wavelength
.lambda.a for collective pumping, and inputted to the optical
amplifier 22b for collective amplification. Here, .lambda.a differs
from any wavelength in .lambda.1L.
[0511] FIG. 41 is a diagram showing an internal structure of the
first repeating station 70b according to the second modification of
the third embodiment of this invention. In FIG. 41, parts
designated by like reference characters have like or corresponding
functions described above, further descriptions of which are thus
omitted.
[0512] Inputted light (.lambda.L+.lambda.a+.lambda.d) from the
transmitting station 20j is branched into three directions; toward
a reflecting means (reflecting element 1) 11a, a fifth filter
(filter 5) 65a and a seventh filter (filter 7) 35e, by an optical
coupler 50 (not shown). The reflecting means 11a reflects only
.lambda.a, thus only (.lambda.1L+.lambda.d) components are inputted
to a first filter 31d. Only an optical signal component .lambda.L
is extracted by the first filter 31d, multiplexed with pumping
light .lambda.c, multiple-wavelength collective-optical-amplified
by a first optical amplifier 31a, and transmitted along with
residual pumping light to the second repeating station 70b'.
[0513] The residual pumping light .lambda.d reflected by the
reflecting means 11a in the transmitting station 20j is extracted
by the fifth filter 65a, and its input level is monitored by a
third optical detector 65b.
[0514] Only residual pumping light .lambda.a of the transmitting
station 20j is extracted by the seventh filter 35e, and its input
is monitored by a fifth optical detector 35d. When the input dies
out, it is determined that the optical cable between the
transmitting station 20j and the first repeating station 70b is
cut. As shown in FIG. 41, transmission light to the transmitting
station 20j has (.lambda.R"+.lambda.d+.lambda.a) components. When
the optical cable between the transmitting station 20j and the
first repeating station 70b is cut, this transmission light is
returned as it is to the first repeating station 70b. In such case,
a level of .lambda.d does not fall. Additionally, .lambda.R" has
the same wavelength as the transmission optical signal .lambda.L
from the transmitting station 20j. For this, they cannot be used as
elements to detect cut.
[0515] On the other hand, .lambda.a loses its supply source, thus
its level falls. For this, by detecting disconnection of this
.lambda.a component, it is possible to detect cut of the optical
cable. Incidentally, inputted light from the first repeating
station 70b is similar.
[0516] FIG. 42 is a diagram showing an internal structure of the
second repeating station 70b' according to the second modification
of the third embodiment of this invention. In FIG. 42, parts
designated by like reference characters have like or corresponding
functions described above, further descriptions of which are thus
omitted.
[0517] Inputted light (.lambda.L'+.lambda.c+.lambda.f) from the
first repeating station 70b is branched into three directions;
toward a reflecting means (reflecting element 1) 11a, a fifth
filter (filter 5) 65a and a seventh filter (filter 7) 35e, by an
optical coupler 50 (not shown) disposed at the entrance's side. The
reflecting means 11a reflects only .lambda.c, thus only
(.lambda.L'+.lambda.f) are inputted to a first filter 31d. Only an
optical signal component .lambda.L' is extracted by the first
filter 31d, multiplexed with pumping light .lambda.e, inputted to a
first optical amplifier 31a,
multiple-wavelength-collective-amplifie- d, and transmitted along
with residual pumping light to the receiving station 40. Residual
pumping light .lambda.f reflected by the reflecting means 11b in
the first repeating station 70b is extracted by the fifth filter
65a, and its input level is monitored by a third optical detector
65b.
[0518] Only the residual pumping light .lambda.c of the first
repeating station 70b is extracted by the seventh filter 35e, and
an input thereof is monitored by a fifth optical detector 35d. When
the input dies out, it is determined that the optical cable between
the first repeating station 70b and the second repeating station
70b' is cut. Transmission light (.lambda.R'+.lambda.f+.lambda.a) is
sent to the first repeating station 70b. When the optical cable
between the first repeating station 70b and the second repeating
station 70b' is cut, this transmission light is returned as it is
to the second repeating station 70b'. In such case, the level of
.lambda.f does not fall. Additionally, .lambda.R' has the same
wavelength as the transmission light optical signal .lambda.L' from
the first repeating station 70b. For this, they cannot be used as
elements to detect cut. On the other hand, .lambda.c loses its
supply source, and its level falls. By detecting disconnection of
inputs of .lambda.c, it is possible to detect cut of the optical
cable. Inputted light from the receiving station 40 is similar.
[0519] With the above structure, the transmitting station 20j
(refer to FIG. 40) performs a process with optical signals as
follows. The transmitting station 20j collectively amplifies and
transmits transmission light .lambda.L to the first repeating
station 70b. Only a .lambda.a component is extracted by a first
loopback filter 23a, the output optical level is monitored by a
first optical detector 23b, returned light .lambda.a from the first
repeating station 70b is extracted by a fifth filter 24a and
monitored by a second optical detector 24b, an actual transmission
loss is calculated on the basis of a difference in optical level
between the first optical detector 23b and the second optical
detector 24b, and the output level of the first pumping source 22d
is adjusted by the controlling means 25 so as to yield the optimum
optical output level.
[0520] With regard to reception, reception light .lambda.R"
(transmission light from the opposite station being collectively
referred as .lambda.R) from the opposing first repeating station
70b is inputted to an optical coupler 51, and split into each
wavelength. The optical signals are inputted to the receiving unit
21a-1, the receiving unit 21a-2, . . . , and the receiving unit
21a-n, respectively, whereby communication between the transmitting
station 20j and the receiving station 40j is established.
[0521] Further, pumping light .lambda.d to the transmitting station
20j is reflected by the reflecting means 11a in the first repeating
station 70b, and the reflected .lambda.d is monitored by a fifth
optical detector (photodiode 5) 26b. When its input level falls,
cut of the optical cable between the transmitting station 20j and
the first repeating station 70b is detected.
[0522] As this, communication is performed among the stations using
only the optical cables in one system, and the output level of the
pumping source is automatically controlled in each of the stations,
which allows the optimum communication.
[0523] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect cut of the optical cable. This remarkably improves
reliability and safety of the optical system 10p.
[0524] (C3) Description of Third Modification of Second Embodiment
of the Invention
[0525] FIG. 43 is a diagram showing a structure of an optical
system according to a third modification of the third embodiment of
this invention. An optical system 10q shown in FIG. 43 is in the
multiple wavelength collective amplification system, which
comprises a transmitting station 20k, a first repeating station
70b, a second repeating station 70b' and a receiving station 40k.
FIG. 44 is a diagram showing an internal structure of the first
repeating station 70b according to the third modification of the
third embodiment of this invention.
[0526] The first repeating station 70b differs from that according
to the second modification of the second embodiment described above
in that data for monitoring a reception level of a fifth optical
detector 35d and data for monitoring a reception level of a sixth
optical detector 36d are inputted to both a first pumping light
controlling means 66b and a second pumping light controlling means
64b. Whereby, cut of the optical cable can be detected.
[0527] A second filter 32b is disposed on the output's side of a
first optical amplifier 31a to extract first pumping light
(.lambda.c) outputted from the first optical amplifier 31a. A first
optical detector 32c detects a level of the first pumping light
(.lambda.c) outputted from the second filter 32b. An eighth filter
36e extracts residual pumping light (.lambda.f) from a received
optical signal, and outputs it. The sixth optical detector 36d
detects the residual pumping light (.lambda.f) from the eighth
filter 36e. Likewise, an output level of the first optical
amplifier 31a is controlled on the basis of a detected level of the
first optical detector 32c, a detected level of a second optical
detector 64b and a detected level of the sixth optical detector
36d.
[0528] Similarly, a fourth filter (filter 4) 67a is disposed on the
output's side of a second optical amplifier 33c to extract second
pumping light (.lambda.d) outputted from the second optical
amplifier 33c. A fourth optical detector (photodiode 4) 67b detects
a level of the second pumping light (.lambda.d) outputted from the
fourth filter 67a. A seventh filter 35e extracts residual pumping
light (.lambda.a) from a received optical signal, and outputs it. A
fifth optical detector 35d detects the residual pumping light
(.lambda.a) from the seventh filter 35e. An output level of the
second optical amplifier 33c is controlled on the basis of a
detected level of the fourth optical detector 67b, a detected level
of the third optical detector 65b and a detected level of the fifth
optical detector 35d.
[0529] In FIGS. 43 and 44, parts designated by like reference
characters have like or corresponding functions described above,
further descriptions of which are thus omitted.
[0530] Flow of an operation of the first pumping light controlling
means 66b shown in FIG. 44 is as described in (s1) to (s6) below.
Flow of an operation of the second pumping light controlling means
64b is similar. (s1) The first pumping light controlling means 66b
detects a difference in reception light level between the first
optical detector 32c and the second optical detector 64b, and
monitors a reception level of the sixth optical detector 36d. (s2)
When the reception level of the sixth optical detector 36d is
constant (while cut is not detected), the first pumping light
controlling means 66b calculates an actual transmission loss
between the first repeating station 70b and the second repeating
station 70b' from (s1), and so controls a first pumping source 66a
as to yield the optimum optical amplified output. (s3) When the
reception level of the sixth optical detector 36d falls (while cut
is detected), the first pumping light controlling means 66b
fluctuates the bias current or the like of the first pumping source
66a. The output level of the pumping light .lambda.c thereby
fluctuates, it is determined that the optical cable is cut after a
relationship between the fluctuation in optical level of the second
optical detector 64b (optical level reflected by the cross section
of the optical cable and returned) and the fluctuation in level of
the pumping light output.
[0531] As this, an accurate control becomes possible, and a more
precise operation becomes possible. Further, communication is
performed among the stations using only the optical cables in one
system, and the output level of the pumping source is automatically
controlled in each of the stations, which allows the optimum
communication.
[0532] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect cut of the optical cable. This remarkably improves
reliability and safety of the optical system 10q.
[0533] (C4) Description of Fourth Modification of Third Embodiment
of the Invention
[0534] FIG. 45 is a diagram showing a structure of an optical
system according to a fourth modification of the third embodiment
of this invention. An optical system 10r shown in FIG. 45 is in the
multiple wavelength collective amplification system, which
comprises a transmitting station 20n, a first repeating station
70d, a second repeating station 70d' and a receiving station 40n.
FIG. 46 is a diagram showing an internal structure of the first
repeating station 70d according to the fourth modification of the
third embodiment of this invention. The first repeating station 70d
and the second repeating station 70d' are almost the same as those
described in the second modification (refer to FIG. 33) of the
second embodiment, where a controlling method using an alarm signal
is added. In FIGS. 45 and 46, parts designated by like reference
characters have like or corresponding functions described above,
further descriptions of which are thus omitted.
[0535] A first optical detector 32c is disposed on the output's
side of a first optical amplifier 31a to detect a level of first
pumping light (.lambda.c) outputted from the first optical
amplifier 31a. A second alarm signal detecting means 68c detects
first pumping light (.lambda.c), on which a modulation signal has
been superimposed, outputted from the optical receiving apparatus's
side (receiving station 40n), and outputs a first alarm signal to
the outside. A fourth optical detector 34c is disposed on the
output's side of a second optical amplifier 33c to detect a level
of second pumping light (.lambda.d) outputted from the second
optical amplifier 33c.
[0536] Further, a first alarm signal detecting means 68a detects
the second pumping light (.lambda.d), on which a modulation signal
has been superimposed, sent from the optical transmitting
apparatus's side (transmitting station 20n in FIG. 45), and outputs
a second alarm signal to the outside. The first alarm signal
communication controlling means 69a outputs a port switching signal
when detecting that first residual pumping light (.lambda.f) sent
from the optical receiving apparatus's side is not inputted in
order to superimpose a modulation signal on a first pumping source
66a and input it. Second optical switches 71a and 71b are connected
to the first pumping source 66a to be able to select whether the
first pumping light (.lambda.c) from the first pumping source 66a
is led to the input's side of the first optical amplifier 31a or
the first pumping light (.lambda.c), on which the modulation signal
has been superimposed, is led to the output's side of the first
optical amplifier 31a according to the port switching signal
outputted from the first alarm signal communication controlling
means 69a.
[0537] A second alarm signal communication controlling means 69b
outputs a port switching signal when detecting that a second
residual pumping light (.lambda.d) sent from the transmitting
station 20n is not inputted in order to superimpose a modulation
signal on a second pumping source 64a and output it. First optical
switches 71c and 71d are connected to the second pumping source 64a
to be able to select whether the second pumping light (.lambda.d)
from the second pumping source 64a is led to the input's side of
the second optical amplifier 33c or the second pumping light
(.lambda.d), on which the modulation signal has been superimposed,
is led to the output's side of the second optical amplifier 33c
according to the port switching signal outputted from the second
alarm signal communication controlling means (69b).
[0538] With the above structure, the transmitting station 20n shown
in FIG. 45 detects a difference in reception optical level between
a first optical detector 23b and a second optical detector 24b in
the normal state, calculates an actual transmission loss between
the transmitting station 20n and the first repeating station 70b. A
controlling means 25 controls a first pumping source 22d so as to
yield the optimum optical amplified output. The reception level of
a fifth optical detector 26b is monitored.
[0539] When the reception level of the fifth optical detector 26b
is constant, namely, while cut is not detected, the above operation
is performed. When the reception level of the fifth optical
detector 26b falls (while cut is detected), an alarm signal
communication control unit 13 controls optical switches 12a and 12b
to switch a route {circle over (1)} in the normal state to a route
{circle over (2)}, modulates the first pumping source 22d, and
transmits an alarm signal in a specific pattern to the first
repeating station 70d along the route {circle over (2)}.
[0540] An alarm signal detecting unit 26d monitors whether the
alarm signal is inputted to the second optical detector 26b. When
the optical cable is cut, the alarm signal obtained by modulating
the pumping light is reflected by the cross section and returned to
its own station. After detection of the alarm signal is confirmed,
cut of the optical cable is determined.
[0541] The first repeating station 70d shown in FIG. 46 is similar.
Inputted light (.lambda.L+.lambda.a+.lambda.d) from the
transmitting station 20n is branched into three directions; toward
a reflecting means 11a, a fifth filter 65a and a seventh filter
35e, by an optical coupler 50 (not shown) disposed on the
entrance's side. The reflecting means 11a reflects only .lambda.a,
thus only (.lambda.L+.lambda.d) components are inputted to a first
filter 31d. Only an optical signal component .lambda.1L is
extracted by the first filter 31d, multiplexed with pumping light
.lambda.c, inputted to the first optical amplifier 31a, and
transmitted along with residual pumping light to the second
repeating station 70d'.
[0542] A first loopback filter 32b extracts only a .lambda.c
component, and the first optical detector 32c monitors a level of
.lambda.c. A first pumping light controlling means 66b calculates
an actual transmission loss between the first repeating station 70d
and the second repeating station 70d' on the basis of a difference
between this level and a level of the returned pumping light
.lambda.c (monitored by a second optical detector 64b) from the
second repeating station 70b', and so controls the first pumping
source 66a as to yield the optimum output.
[0543] The fifth filter 65a extracts residual pumping light
.lambda.d reflected by the reflecting means 11a in the transmitting
station 20n, and a third optical detector 65b monitors its input
level. A second pumping light controlling means 64b calculates an
actual transmission loss between the transmitting station 20n and
the first repeating station 70d, and controls so that an output of
the second pumping source 64a becomes optimum.
[0544] And the more, in the direction from the first repeating
station 70d to the transmitting station 20n, only residual pumping
light .lambda.a of the transmitting station 20n is extracted by the
seventh filter 35e, and its input is monitored by a fifth optical
detector 35d. When the input dies out, the alarm signal
communication control unit 69b controls the optical switches 71c
and 71d, switches a port P1 in the normal state to a port P2,
modulates the second pumping source 64a, and transmits an alarm
signal in a specific pattern to the transmitting station 20n from
the port P2. An alarm signal detecting unit 68a monitors whether
the alarm signal is inputted to the third optical detector
(photodiode 3) 65b. When the optical cable is cut, the alarm signal
obtained by modulating the pumping light is reflected by the cross
section, and returned to its own station. After detection of the
alarm signal is confirmed, cut of the optical cable is
determined.
[0545] As this, an accurate control becomes possible, and a more
precise operation becomes possible. Further, communication is
performed among the stations using only the optical cables in one
system, and the output level of the pumping source is automatically
controlled in each of the stations, which allows the optimum
communication.
[0546] As this, the installation cost and maintenance cost of the
optical cables are largely decreased, and each of the stations can
detect cut of the optical cable. This remarkably improves
reliability and safety of the optical system 10r.
[0547] (D) Others
[0548] As above-described, in the first embodiment, the second
embodiment, the third embodiment and their modifications, the
optical couplers 50 or the like are not shown in the drawings
except FIG. 2. The multiplexing and demultiplexing are foregoing
realized by using an optical fiber of a fusion type, but another
element may be used.
[0549] Further, it is possible to combine the detection modes and
the control modes in the embodiments and modifications. In
concrete, they may be combined in consideration of many variations
such as (t1) to (t6) below. Note that the superiority of the
present invention is not spoiled even when a way of combining these
is changed.
[0550] (t1) the number of stages of the repeating stations;
[0551] (t2) with respect to adjustment of the output level of the
pumping source in the transmitting station or the receiving
station, presence/absence of the adjusting control or the
controlling mode;
[0552] (t3) with respect to adjustment of the output level of the
pumping source in the repeating station, presence/absence of the
adjusting control or the controlling mode;
[0553] (t4) with respect to adjustment of the output level of EDFA
in the repeating station, presence/absence of the adjusting control
or the controlling mode;
[0554] (t5) with respect to the disconnect detecting method in the
transmitting station or the receiving station, presence/absence of
it or the controlling mode; and
[0555] (t6) with respect to the disconnect detecting method in the
repeating station, presence/absence of it or the controlling
mode.
[0556] In FIG. 4, the second repeating station 30c' has a similar
structure to the first repeating station 30c, excepting differences
in subscript of the optical wavelengths, for example, between
.lambda.1R and .lambda.1R', .lambda.1R' and .lambda.1R", and the
like.
[0557] The inside of the second repeating station 30b' shown in
FIG. 7 is similar to that of the first repeating station 30b shown
in FIG. 8.
[0558] Industrial Applicability
[0559] As above, according to this invention, transmission light
and reception light can be transmitted through optical fiber cables
in one system, thus the installation cost and maintenance cost of
the optical cable cost can be decreased. Detection of cut of the
optical cables is performed using the monitoring function with
pumping light and residual pumping light in two-way transmission,
which remarkably improves reliability and safety of the system.
Further, adjustment of the optical output level in the repeating
station is most suitably set according to an actual transmission
distance, which allows an efficient system operation.
* * * * *